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Composites Science and Technology
Journal Prestige (SJR): 1.702
Citation Impact (citeScore): 6
Number of Followers: 195  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0266-3538
Published by Elsevier Homepage  [3162 journals]
  • High temperature rheological behavior and sintering kinetics of CF/PEEK
           composites during selective laser sintering
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Mengxue Yan, Xiaoyong Tian, Gang Peng, Dichen Li, Xiaoyu Zhang As a kind of high performance polymer with excellent mechanical strength, high temperature property and chemical resistance, the polyether-ether-ketone (PEEK) and its composites are the promising candidates that can satisfy the demands for high stiff and lightweight in aerospace industry. So it is very attractive to fabricate PEEK and its composites parts with additive manufacturing technology, especially the selective laser sintering (SLS), due to its advantage on the fabrication of the parts with complex geometries. However, the strengths of the PEEK and its composites prepared by SLS are obviously lower than their injection molded parts and the laser sintering kinetics of the PEEK composites is seldom studied. In this paper, to fabricate the carbon fibers (CF) reinforced PEEK composites with high strength by SLS, the sintering kinetics of CF/PEEK composites was thoroughly studied based on the high temperature rheological behavior. A novel effective melting zone was defined by combining the simulated temperature distribution with the viscosity-temperature relationship and used to predict the process planning. Finally, the calculation results were validated by employing the simulation parameters in experiments and the tensile strength of CF/PEEK composites reached 109 ± 1 MPa with an elasticity modulus of 7365 ± 468 MPa, which is 85% higher than injection molded pure PEEK. Therefore, methods in this work could be considered as a complement to the numerical analysis of SLS process and the reinforced CF/PEEK composites may be used in aerospace industry for the structure optimization and lightweight design with complex geometries.
       
  • Effects of inter-ply angles on the failure mechanisms in bioinspired
           helicoidal laminates
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): J.L. Liu, H.P. Lee, V.B.C. Tan Following encouraging findings on the potential of helicoidal laminates under transverse loads to significantly outperform cross-ply laminates, a more extensive study was undertaken to include thicker helicoidal laminates with the greater range of variation in inter-ply angles. Previous research has shown that thin helicoidal laminates outperform cross-ply laminates when the inter-ply angle is less than 10°. It was reported that the small inter-ply angles in helicoidal laminates make them more resistant to delamination. Consequently, less delamination occurs and they are deeper inside the laminates. This delays catastrophic failure, which occurs when transverse cracks propagating from the surface of the laminates merges with the delamination. The current study shows that thick helicoidal laminates with small inter-ply angles promote a different damage mechanism not apparent in thin laminates. Hence reducing inter-ply angles does not always lead to higher transverse load bearing capability. Observations from CT scan images of thick helicoidal laminates suggest that higher delamination resistance offered by small inter-ply angles is offset by the ease with which cracks between fibers propagates transversely when the angle is too small. Hence, helicoidal laminates comprising 73 plies of unidirectional carbon fiber reinforced laminas with 2.5° inter-ply angle could not achieve the peak loads of 73-ply laminates with 10° inter-ply angle. The optimal inter-ply angle to achieve high peak load appears to be between 5° to 10°. This study shows that the peak transverse load for helicoidal laminates can be up to 73% higher than that of cross-ply laminates when they are optimized.
       
  • Thermal conductivity of polypropylene/aluminum oxide nanocomposites
           prepared based on reactor granule technology
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Bulbul Maira, Kengo Takeuchi, Patchanee Chammingkwan, Minoru Terano, Toshiaki Taniike A reactor granule technology (RGT) is a new method for the in-situ fabrication of polyolefin-based nanocomposites. It involves the impregnation and confinement of inorganic molecular precursors in the porosity of polyolefin reactor granule, and subsequent conversion of the precursors into highly dispersed inorganic nanoparticles during melt processing. In this contribution, the RGT was applied to develop thermally conductive polypropylene (PP)/aluminum oxide (Al2O3) nanocomposites with the aid of two strategies. By melt-blending highly filled reactor granule with unfilled reactor granule, filler-rich and polymer-rich domains were created at around 10 μm scale, in which the filler-rich domains offered a thermally conductive pathway. The other strategy was based on tailoring the interfacial interaction between PP and Al2O3: An aluminum alkoxide precursor and a silane coupling agent were co-impregnated and converted into organically modified Al2O3 nanoparticles. Both of the strategies successfully improved the thermal conductivity of the nanocomposites at a fixed Al2O3 loading. The highest enhancement was achieved based on the interfacial modification using (2-phenylethyl)trimethoxysilane, where the thermal conductivity reached 0.74 W/m K at 20 wt% compared to 0.21 W/m K for pristine PP.
       
  • Using variable interfacial adhesion characteristics within a composite to
           improve flexural strength and decrease fiber volume
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Filip Stojcevski, James D. Randall, Luke C. Henderson This paper investigates the impact of using amine functionalised fibers in composite “hybrid” laminates to improve interfacial shear strength (IFSS) and reduce laminate weight. A comparison of single fiber fragmentation testing (SFFT) and short beam shear testing (SBS) showed that 103.6% improvements of IFSS at a single fiber level only translate to a 23.3% improvement in SBS testing. However, localised use of both functionalised and non-functionalised T300 fibers in a “hybrid interface” laminate improved IFSS by 56.7%. Hence this study shows that careful placement of fibers and localised manipulation of the interface characteristics can be used to great effect when designing a composite material. Ultimately, the use of a hybrid interface approach was able to provide a weight reduction of 11.27% while not sacrificing flexural strength compared to the baseline T300 fibers.
       
  • Optimal synergy between micro and nano scale: Hierarchical all carbon
           composite fibers for enhanced stiffness, interfacial shear strength and
           Raman strain sensing
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kyriaki Tsirka, Lazaros Tzounis, Apostolos Avgeropoulos, Marco Liebscher, Viktor Mechtcherine, Alkiviadis S. Paipetis Multifunctional hierarchical reinforcements are fabricated by growing multi walled carbon nanotubes (CNTs) onto carbon fibers (CFs) via chemical vapor deposition. In contrast to typical hybrid multi scale reinforced composites, the biomimetic approach of hierarchical interconnection between CFs and CNTs is followed in order to provide the dimensional confinement required for the effective synergy between the nanophase i.e. the CNTs and the micron phase i.e. the CFs. Compared to the reference CF: (i) ASTM single fiber tensile tests reveal up to 50% increase in tensile modulus together with the expected decrease in tensile strength, (ii) Single Fiber Fragmentation Tests (SFFT) reveal up to 134% enhancement for Interfacial Shear Strength (IFSS), (iii) the frequency of the Raman 2D graphitic vibrational mode with strain shows a strain sensitivity enhancement up to 87.4% and (iv) fractographic investigation shows bridging of the CNTs only for specific growth conditions, which correspond to the optimal IFSS. Furthermore, a direct correlation between the Raman strain sensitivity with the young moduli of the CF and the hierarchical CF-CNT is found, proving the efficient stress transfer from the nano to micron scale in a “composite” fiber. Overall, an optimal synergy between the reinforcing graphitic phases is achieved, attaining for the first time an equivalent stiffness for the CNT reinforcement close to theoretically obtained values. Thus, biomimetic hierarchical reinforcements provide the roadmap for the full exploitation of the unique properties of the nanophase in advanced structural composites.
       
  • Design of super-tough co-continuous PLA/NR/SiO2 TPVs with balanced
           stiffness-toughness based on reinforced rubber and interfacial
           compatibilization
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yutong Liu, Liming Cao, Daosheng Yuan, Yukun Chen Elastomer has been proved to be a prominent toughener for polylactide (PLA), however, the remarkable increase in toughness always accompanies a sharp decrease in tensile strength. In this work, based on rubber reinforcement theory and interfacial compatibilization technique, co-continuous PLA/natural rubber (NR)/silica (SiO2) thermoplastic vulcanizates (TPVs) with balanced stiffness and toughness were designed. By employing thermodynamic and kinetic factors, SiO2 was restricted to distribute in rubber phase or at the interface due to the strong physical entanglements between NR and SiO2, which played a significant role in reinforcing rubber and interfacial compatibilization. As a result, impact strength of the TPVs was greatly improved without decrease in tensile strength. With 12.5 phr SiO2, impact strength increased to 85.1 kJ/m2 (without fracture), which was 8 times of blank sample and 30 times than that of neat PLA, respectively. In addition, the influence of reinforced rubber, superior interfacial adhesion on fracture toughness and deformation mechanism were investigated semi-quantitatively under digital Izod impact tests.Graphical abstractImage 1
       
  • EMI shielding properties of laminated graphene and PbTiO3 reinforced
           poly(3,4-ethylenedioxythiophene) nanocomposites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Jasvir Dalal, Sushma Lather, Anjli Gupta, Sajjan Dahiya, A.S. Maan, Kuldeep Singh, S.K. Dhawan, Anil Ohlan In this paper, PEDOT/reduced graphene oxide (RGO)/PbTiO3 nanocomposites have been synthesized using facile insitu chemical oxidative polymerization method. The synthesis method leads to the formation of core-shell structured nanocomposites containing PbTiO3 as primary filler and RGO as secondary filler in PEDOT matrix. The core-shell morphology of the composites has been confirmed using transmission electron microscope with average particle size 20–30 nm observed for PbTiO3. The incorporation of RGO and PbTiO3 in the PEDOT matrix has been confirmed by X-ray diffraction. A systematic study on electromagnetic shielding properties and the effect of PbTiO3 concentration on different properties has been carried out. The ferro-electric PbTiO3 with RGO induced dielectric loss in the composites, whereas, PEDOT establish a conducting network over RGO layer and PbTiO3 nanoparticles that improve electromagnetic shielding properties by increasing the dielectric loss. As a result, an enhanced electromagnetic shielding effectiveness value of 51.94 dB (>99.999% attenuation) has been achieved in 12.4–18 GHz frequency range. The nanocomposites were further characterized using Fourier transmission infrared spectroscopy and thermal gravimetric analysis.
       
  • A high resolution method for characterisation of fibre misalignment angles
           in composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): D. Wilhelmsson, L.E. Asp In this paper a novel method to characterise fibre waviness in composites is presented and assessed. The proposed method referred to as the “high resolution misalignment analysis” (HRMA) method and is suitable for measurements with high spatial resolution. The HRMA method measures misalignment angles tracing individual fibres in detailed micrographs. Here, the method is evaluated using software-generated images with known statistics to mimic real micrographs. Results reveal that the HRMA method provides very accurate measurements on composites with high fibre waviness, outperforming existing methods, whereas it performs on par with existing methods for materials featuring medium fibre waviness. The HRMA method is capable of characterising a 2 cm2 micrograph with a spatial resolution of 55 μm in approximately 1 min on a standard laptop computer. The HRMA code and software-generated images are supplied as supplementary material to this paper.
       
  • Effect of elastic modulus mismatch of epoxy/titanium dioxide coated silver
           nanowire composites on the performance of thermal conductivity
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yunliang Jiang, Maoyuan Li, Chao Chen, Zhigang Xue, Xiaolin Xie, Xingping Zhou, Yiu-Wing Mai The effect of elastic modulus mismatch of epoxy/silver nanowires (epoxy/AgNWs) composites on thermal conductivity was critically evaluated by synthesizing a stiff titanium dioxide (TiO2) coating on the surface of AgNWs (designated as AgNWs@TiO2) with different length/diameter aspect ratio. Compared to epoxy/AgNWs composites, AgNWs@TiO2 could be more uniformly dispersed in epoxy matrix. However, the TiO2 intermediate layer with a higher elastic modulus increased the modulus mismatch with epoxy, exacerbating the interfacial phonon scattering, and the thermal conductivity of the epoxy/AgNWs@TiO2 composites was decreased. Moreover, the epoxy/AgNWs@TiO2 composites possessed enhanced volume electrical resistivity and reduced dielectric properties relative to the epoxy/AgNWs composites. These observed results on thermal conductivity, electrical insulation, dielectric loss and dielectric constant due to TiO2-coated AgNWs are more prominently displayed at higher nanowire loading (4 vol%) and aspect ratio (1000).
       
  • High performance glass fiber reinforced polypropylene realized by reactive
           extrusion technology
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Guojun Luo, Gang liu, Yunlei Chen, Wenbin Liang, Guogang Liu, Yanhua Niu, Guangxian Li High performance polypropylene/glass fiber (PP/GF) composites were prepared by introducing different percentage of maleic anhydride-g-polypropylene (MPP) and epoxy resin (EP) in the matrix. The coupling effect of MPP and EP on the mechanical properties of the hybrid composites were highlighted and the complicated reinforcing mechanism were discussed in detail. Even though the addition of MPP could apparently improve the performance of composites, as the EP coupled especially at higher MPP and EP content, both the tensile and impact strength get further enhancement. For the sample with 10 wt% MPP and 10 wt% EP (10MPP/10EP), the tensile and impact strength show significant enhancement by 136% and 171%, respectively, compared to the control PP/GF composite. It is demonstrated that the good compatibility among each constituent as well as the reaction between EP and MPP, which could efficiently facilitate the network formation, contribute to the high performance of the composites. The finer EP particles caused by the enhanced compatibility as nucleating agent could promote the crystallization, but the crystallinity of the composites does not change so much. A schematic mechanism of the interfacial structure on both molecular and microscopic levels is depicted, where the reaction between MPP and EP are considered as a dominated factor to influence the above-mentioned network formation. This local network structure causes the composites as an integrate showing excellent mechanical performance.
       
  • Multi-dimensional strain sensor based on carbon nanotube film with aligned
           conductive networks
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Lifeng Ma, Wei Yang, Yansong Wang, Hao Chen, Yanfen Xing, Jincheng Wang Carbon nanotubes (CNTs) show a tremendous promise on strain sensor applications, but the stretchable ability of CNT devices is low due to their poor ductility. Herein, novel aligned conductive networks of CNT film were designed and introduced onto polydimethylsiloxane (PDMS) substrate, which realized highly stretchable multi-dimensional strain sensitivity up to a strain of 260% and an excellent cyclical durability. The gauge factor (GF) along the CNT aligned direction, i. e. A direction, can reach 461 up to a strain of 260% while the resistance of the perpendicular direction (B direction) keeps almost the same with initial value, showing a multi-dimensional strain detection capability. The high GF along A direction of the CNT film is caused by the slippage, damage and rupture of CNT bundles with strain increasing, while the CNT entanglement between the adjacent CNTs stabilizes the resistance along B direction. This study rationalizes the aligned CNT network concept to realize the multi-dimensional strain sensors, which have a great potential to be applied in complex strain detection in practical applications.Graphical abstractImage 1
       
  • Microwave-assisted hydrosilylation of polypropylene and its application to
           in-situ grafted polypropylene/SiO2 nanocomposites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Patchanee Chammingkwan, Masahito Toyonaga, Toru Wada, Minoru Terano, Toshiaki Taniike Grafting end-functionalized polypropylene (PP) to the surfaces of nanoparticles is a promising approach in boosting physical properties of PP-based nanocomposites. In this study, a practical pathway is presented for the fabrication of PP-grafted nanocomposites: Reactive silicon alkoxy groups were introduced through microwave-assisted hydrosilylation of terminal unsaturation of vis-breaking PP. Thus obtained hydrosilylated PP was added as a reactive additive in melt compounding of PP with SiO2 nanoparticles to implement in-situ grafting. Significant improvements were attained in the dispersion of SiO2 nanoparticles, the crystallization rate and the tensile strength.
       
  • Multi-functional composite aerogels enabled by chemical integration of
           graphene oxide and waterborne polyurethane via a facile and green method
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Furong Sun, Jiyu Yang, Huan Zhang, Longfei Yi, Kaijun Luo, Lijuan Zhao, Jinrong Wu Practical thermal-insulating applications require aerogels to possess multi-functionality in addition to a low thermal conductivity. However, it is still a challenge to fabricate multi-functional aerogels. Here we use an environmentally friendly method to obtain multi-functional hybrid aerogels by chemical integration of waterborne polyurethane (WPU) and graphene oxide (GO). In the hybrid aerogels, covalent networks are formed in WPU itself and between WPU molecules and GO sheets through the deblocking and condensation reactions, while physical networks are formed by stacking between GO sheets and phase separation in WPU. The existence of both physical and chemical networks imparts high mechanical property and excellent shape-memory capability to the hybrid aerogels. The interfaces between different networks play a role of phonon-scattering, thus enabling a low thermal conductivity for the hybrid aerogels. Moreover, rough structures on the surface endow the hybrid aerogels with high hydrophobicity. The multi-functionality properties presented in this paper provide a potential usage of aerogels with a wide range of thermal-insulating characteristics which can improve the energy efficiency effectively.
       
  • Polypropylene-based ternary nanocomposites for recyclable high-voltage
           direct-current cable insulation
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yao Zhou, Bin Dang, Haoming Wang, Jiping Liu, Qi Li, Jun Hu, Jinliang He Polymeric high-voltage direct-current (HVDC) cables are the core equipment in energy internet, which enable the long-distance large-capacity electric power transmission, large-scale utilization of renewable electric power and flexible interconnection of large power grids. Performance of the HVDC cables are determined by the properties of their insulation material. However, the traditional polymeric HVDC cable insulation material, crosslinking polyethylene (XLPE) is limited to relatively low working temperature which restricts the power capacity of HVDC cables. XLPE with thermosetting characteristics also presents a major barrier to material recycling and environmental pollution reduction. Here we report the ternary nanocomposites of polypropylene (PP), thermoplastic polyolefin (TPO) and MgO nanoparticles as an efficient way to recyclable HVDC cable insulation material that simultaneously possess excellent thermal, mechanical and electrical properties, especially at high temperatures. At an optimal composition, the ternary nanocomposites integrate the complementary properties of the multi-components to raise the mechanical flexibility at room temperature and greatly improve the electrical properties at high temperatures (including suppressed space charge accumulation and increased breakdown strength and volume resistivity) while retaining high melting temperature comparable to PP of about 160 °C. This work may pave a way for synergistic optimization of the overall properties of insulation materials and enabling the successful development of recyclable insulation material for large-capacity HVDC cable application.
       
  • Core-shell flame retardant/graphene oxide hybrid: a self-assembly
           strategy towards reducing fire hazard and improving toughness of
           polylactic acid
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Jian Jing, Yan Zhang, Zheng-Ping Fang, De-Yi Wang Biobased flame retardant/graphene oxide hybrid (GOH) as a multifunctional flame retardant for polylactic acid (PLA) was synthesized through organic-solvent-free self-assembly. The electrostatic interactions deposited the polyethylenimine (PEI) and biobased polyelectrolyte (BPE) coating on the surface of ammonium polyphosphate (APP) in water, which gave the negatively charged core-shell flame retardant. Then, GOH was obtained via aqueous self-assembling between the positively charged graphene oxide (pGO) obtained by grafting pristine GO with PEI and the core-shell flame retardant. Subsequently, GOH was employed as multifunctional flame retardant to PLA, aiming to enhance both flame retardancy and toughness. Based on the investigation via LOI, UL94 test and the cone calorimetry, it clearly showed that GOH endowed PLA significantly enhanced flame retardancy. The flame retardancy of GOH in PLA was performed in both of the gas-phase and condensed-phase mechanisms according to the analysis of the volatile gases and the residues. As for the mechanical properties of PLA/GOH composites, an over 6 folds increment in elongation at break (52.4%) and 86.7% increase in notched impact strength (5.6 kJ/m2) were achieved for PLA/10%GOH, compared with that of the neat PLA. It meant the introduction of GOH remarkably improved toughness of PLA.
       
  • Size effects in layered composites – Defect tolerance and strength
           optimization
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Junjie Liu, Wenqing Zhu, Zhongliang Yu, Xiaoding Wei Mixture of hard and soft phases in a smart way makes strong and tough materials – this approach, inspired by natural composites, has been widely adopted by scientists and engineers. Behind it exist many interesting fundamental mechanics. In this study, we solve analytically the stress intensity factor for a crack propagating from the hard to the soft phase in a layered composite starting with the postulation on the crack profile inspired by the shear-lag model. Our analysis shows that when a crack extends from the hard phase into the soft one, the stress intensity factor amplifies first at the hard-soft interface and then declines quickly to zero as it progresses toward the next hard phase. This crack arresting mechanism works until a secondary crack initiates in the next hard layer and then merges with the main crack. The efficiency of the defect tolerance, measured by the effective strength of the layered composite, is found to exhibit strong size effects. Overall, the smaller the dimensions of two phases are, the more efficiently of the layered composites tolerate defects. Furthermore, if the dimension of one phase is given, there always exists a critical dimension of the other phase that optimizes the efficiency (or the composite strength). A relationship between the defect tolerance efficiency with the nanostructures which is analogous to the famous “Hall-Petch” and “inverse Hall-Petch” relationships for polycrystalline metals is found. The analysis in this work can be used to guide the micro-to nano-structure design for synthesizing innovative defect-tolerant composites.
       
  • Continuous carbon fiber/crosslinkable poly(ether ether ketone) laminated
           composites with outstanding mechanical properties, robust solvent
           resistance and excellent thermal stability
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yunhe Zhang, Wei Tao, Yu Zhang, Lin Tang, Junwei Gu, Zhenhua Jiang Continuous carbon fiber (CCF) reinforced polymeric composites have attracted significant attention in the aeronautic and automobile industries. In this study, novel CCF/poly(ether ether ketone) (PEEK) composites with robust solvent resistance, excellent thermal stability and outstanding mechanical properties were successfully fabricated via a facile solution impregnation process, mainly ascribed to the introduction of the crosslinkable phenylethynyl pendant to PEEK (PEP-PEEK) with excellent solubility. After the crosslinking reaction, PEP-PEEK presented robust solvent resistance, good thermal stability, and high mechanical properties. The longitudinal tensile strength of the CCF/PEP-PEEK composites significantly improved to 1610 MPa, which was 19 times stronger than the longitudinal tensile strength of PEP-PEEK. In the meantime, the CCF/PEP-PEEK composites also had a higher long-term operating temperature, excellent thermal stability and high heat distortion temperature. This study was performed as part of a larger effort to provide a simple and feasible method for the preparation of high quality continuous fiber reinforced poly(ether ether ketone) composites.
       
  • Investigation of ultraviolet radiation effects on thermomechanical
           properties and shape memory behaviour of styrene-based shape memory
           polymers and its composite
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Wessam Al Azzawi, J.A. Epaarachchi, Jinsong Leng In recent years, shape memory polymers (SMP) have been researched extensively for space applications, such as deployable solar panels and antenna reflectors. Space applications cause SMP components to be severely exposed to ultraviolet (UV) light which may results in material degradation which may causes catastrophic failures and costs substantial amount of public money. This paper investigates the effect of UV light exposure on thermomechanical properties and shape memory effect (SME) of the Styrene-based SMP and its Glass fibre shape memory polymer composites (SMPC). Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), have been used to investigate the thermomechanical properties, SMEs and thermal stability before and after the UV exposure. Further, Fourier transform infrared spectroscopy (FTIR) was performed to analyse the after effect of UV exposure on the polymer's chemical structure. Results have revealed that UV exposure had different impacts on the SMP samples. UV exposure have degraded the mechanical properties, lowered the glass transition temperature (Tg), considerably reduced shape recovery rate, and programming and recovery stresses in all samples. However, the exposure had no considerable effect on the fixity ratio and relaxation modulus of the neat SMP sample, and it slightly increased the fixity ratio of the SMPC samples.
       
  • The effect of dual-scale carbon fibre network on sensitivity and
           stretchability of wearable sensors
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Fan Zhang, Shuying Wu, Shuhua Peng, Chun H. Wang Sensitivity and stretchability are two key characteristics of wearable sensors and tactile sensors for soft robotics. Here, we present a new technique to increase the sensitivity of wearable sensors by creating a conductive network of dual-scale carbon fibres, i.e., carbon nanofibres (CNFs) and short carbon fibres (SCFs), in a polydimethylsiloxane (PDMS) matrix. To quantify the effects of this dual-scale carbon fibre network on the stretchability, sensitivity, and stability under repeated loading, comprehensive experiments were conducted to characterise the electrical conductivity, mechanical properties, and piezoresistivity of the resultant PDMS composites with varying concentrations of carbon fibres. The Prony series model of viscoelasticity was adapted to model the strain-rate dependent behaviour of the new sensors. The results reveal that this dual-scale network is able to significantly lower the percolation threshold below that of either of the single-scale composites containing only SCFs or CNFs, indicating a strong synergistic effect. Furthermore, the dual-scale carbon network exhibits higher piezoresistive sensitivity than the CNF-reinforced composite while retaining similar stretchability, thus offering a new technique for creating highly sensitive wearable sensors and tactile sensors for soft robotics.
       
  • Facile method to functionalize graphene oxide nanoribbons and its
           application to Poly(p-phenylene benzobisoxazole) composite
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Mingqiang Wang, Chunyan Wang, Yuanjun Song, Chunhua Zhang, Lu Shao, Zaixing Jiang, Yudong Huang Graphene oxide nanoribbons (GONRs), as a new member of carbon family, attracted extensive attention in industry and science field. It has considered to be as a promising nanomaterial for applications in the field of materials science, energy storage and optics science due to its extraordinary mechanical, electrical and thermal properties. Hence, in this study, we carried out a facile and efficient strategy for preparing poly (phenylene benzobisoxazole) (PBO)/GONRs(PGR) composite fibers via one-pot in situ polycondensation method for enhancement in mechanical and thermal properties. The GONRs sheets in this work were obtained by unwrapping multi-walled carbon nanotubes (MWCNTs) side walls, and then directly reacted with PBO monomer 4,6-diaminoresorcinol(DAR) and covalently grafted on PBO molecular chains. The structure and morphology of GONRs and modified GONRs were well demonstrated by the FT-IR, XPS and TEM analysis for confirming the formation of chemical bond between GONRs and PBO molecular chains. The mechanical and thermal properties of PGR composite fibers were also investigated. It was found that the performance of composite fibers about 32.1% improvement in tensile modulus, 24.2% in tensile strength and 10.5% thermal stability, respectively.
       
  • Experimental and numerical investigation of the needling process for
           quartz fibers
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Junbo Xie, Xiaoming Chen, Yifan Zhang, Guodong Fang, Li Chen This paper investigates the deformation and damage of quartz preforms during the needling process. Effect of needling position and fabric thickness on the resistance force of the needle are experimentally researched. A numerical methodology based on the concept of virtual fibers is proposed to establish the geometry models of 2D broken twill and nonwoven fabrics. Then the needling process of the fabric plies is simulated by finite element method using an explicit dynamics algorithm. Deflection, stretch and breakage of the fibers are analyzed. The simulated fiber architectures of the needling positions are fairly close to the practical observations. Resistance force of the needling process can be predicted with satisfactory accuracy. The aim of the proposed approach is to generate the virtual fiber structure of needled preforms and obtain the effect of needling process on the fiber damage. This approach would be helpful for designing low-damage preforms and improve the mechanical properties of needled composites.
       
  • Improved organic-inorganic/graphene hybrid composite as encapsulant for
           white LEDs: Role of graphene, titanium (IV) isopropoxide and
           diphenylsilanediol
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): P. Madhusudhana Reddy, Chi-Jung Chang, Chun-Feng Lai, Min-Ju Su, Mei-Hui Tsai We report a graphene embedded organic-inorganic hybrid (O-I hybrid) composites that can be utilized as robust encapsulants for white light emitting diodes (WLEDs). The effect of graphene and monomers on the thermal resistance, refractive index (RI), transparency, thermal conductivity, and thermal aging stability of the encapsulant were studied. This study has explicitly unveiled that the embedded graphene played a multifunctional role in producing a high-performance encapsulant. Compared with graphene free O-I hybrid encapsulant, RI, thermal conductivity and heat dissipation ability of the graphene embedded encapsulants were significantly improved. After continuous operation for 10 days, the color rendering index (Ra) of WLED with graphene embedded encapsulants changed from 89.5 to 89.2 (driving current 100 mA), while the correlated color temperature (CCT) altered from 4535 to 4546. Its luminous efficiency changed from 82.9 to 81.2 lm/W. The WLEDs with graphene embedded O-I hybrid encapsulant exhibited long-term stability. This work has paved the way for rational design and assembly of graphene embedded composites as robust materials for various requirements of WLED applications.Graphical abstractImage 1
       
  • Chemical vapor deposition-based grafting of CNTs onto basalt fabric and
           their reinforcement in epoxy-based composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Garima Mittal, Kyong Y. Rhee Basalt fiber (BF) is considered to be a green industrial material, exhibiting outstanding environmental stability along with superior mechanical properties compared to E-type glass fiber. It is also less expensive than carbon fiber, making make it perfect for the mass-production of basalt fiber-reinforced polymer (BFRPs) composites. BFRPs are reinforced with nanomaterials to further enhance their performance. However, nanomaterials have the tendency to agglomerate because of their high surface energy, which hinders their efficient dispersion into the matrix. Hence, in this study, we grafted CNTs onto basalt fabric using chemical vapor deposition (CVD). Furthermore, CNT-grafted basalt fabric (BF-CNT) was sandwiched with epoxy via a hand lay-up technique. XRD, HR-RAMAN, FE-SEM, and thermogravimetric analysis (TGA) were performed to characterize BF-CNT. The properties of the fabricated BF-CNT/epoxy composites were also analyzed and compared with CNT-reinforced BF/epoxy composites. Based on our results, we found that the BF-CNT/epoxy composite shows improved properties.
       
  • Low-velocity impact behaviour of a shear thickening fluid (STF) and
           STF-filled sandwich composite panels
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kunkun Fu, Hongjian Wang, Li Chang, Matthew Foley, Klaus Friedrich, Lin Ye Sandwich composite panels (SCPs) with carbon fibre reinforced plastic (CFRP) facings are usually vulnerable to low-velocity transverse impact loading. In this study, a method is presented to improve the impact resistance and energy absorption capacity of CFRP-faced SCPs by filling them with a concentrated styrene/acrylate particle based shear thickening fluid (STF). First, for the STF alone, aspects of mechanical performance, namely rheological and low-velocity impact behaviours, were systematically examined. It was found that the critical shear stress of the STF was lower than that of silica particle based STF with a similar particle size and volume fraction, indicating that shear thickening was more easily achieved in the styrene/acrylate particle based STF. In addition, the STF exhibited much higher energy absorption capacity than an aluminium foam. Finally, low-velocity transverse impact experiments were performed on STF-filled SCPs with two core thicknesses, 7.2 mm and 12.7 mm. It was shown that the absorbed energy of the SCPs with a thin core increased by up to 99.3%, while the impact damage of SCPs with a thick core could be effectively suppressed on the back surface of the SCPs. The impact mechanism of the STF-filled SCPs is also discussed. This study provides a new method for the design of impact-resistant SCPs.
       
  • Experimental determination of Through-Thickness Compression (TTC)
           enhancement factor for Mode II fracture energy
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Xiaodong Xu, Michael R. Wisnom, Xiaoyang Sun, Tamas Rev, Stephen R. Hallett Mode II fracture energy, GIIC, is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, ηG, for GIIC. A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined ηG can be successfully used to model the effect of TTC on delamination.
       
  • Revisiting the thickness reduction approach for near-foldable capacitive
           touch sensors based on a single layer of Ag nanowire-polymer composite
           structure
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kwang-Seok Kim, Sun Ok Kim, Chul Jong Han, Dae Up Kim, Jin Soo Kim, Yeon-Tae Yu, Cheul-Ro Lee, Jong-Woong Kim Although a percolated network of silver nanowires (AgNWs) is considered the most promising flexible transparent electrode because of its high conductivity, high transmittance, excellent flexibility, and facile patternability, it has encountered a serious delay in its application to most optoelectronic devices. Here, we analyzed the reasons and tried to resolve the current issues to achieve near-foldable transparent touch sensors by employing an inverted layer processing method. A hydroxylated polydimethylsiloxane (PDMS) was used as a preliminary substrate for deposition and patterning of AgNWs, and then the nanowires were completely transferred to the newest version of colorless polyimide (cPI) by hydrophobic recovery of the PDMS surface. For the first time, we designed an automatic apparatus for testing the foldability of the fabricated composite film by a spacer inserting method. The testing of various AgNWs/cPI films with this method revealed that the thickness reduction approach could be an efficient and powerful tool to attain near-foldable electrodes if the AgNWs are solidly adhered to the substrate. Based on these findings, we could successfully demonstrate a near-foldable touch sensor, which is capable of sensing human touches even in the folded state.
       
  • Inter-fibre failure of through-thickness reinforced laminates in combined
           transverse compression and shear load
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Hao Cui, António R. Melro, Mehdi Yasaee Extensive studies have been reported on the improvement of through-thickness reinforcement to inter-laminar performance of composite laminates; current understanding on the in-plane performance is relatively limited, although it is also concerned in industrial application. The influence of through-thickness reinforcement (Z-pinning) on the inter-fibre failure in compression of unidirectional laminates was investigated. Both unpinned and Z-pinned laminates were tested at four different off-axis angles, representing different combinations of transverse compression and in-plane shear stress. It was found that the stiffness of Z-pinned laminates decreased significantly in all off-axis angles. The failure strain and strength were reduced in shear dominated failure modes, while improved in the compression dominated failure modes by the presence of the Z-pins. A further investigation on the angle of failure plane was carried out and a comparison with analytical failure models is presented.
       
  • Electric-field-induced out-of-plane alignment of clay in
           poly(dimethylsiloxane) with enhanced anisotropic thermal conductivity and
           mechanical properties
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Zuqi Liu, Panrui Peng, Zhihong Liu, Wei Fang, Qingzhong Zhou, Xueqing Liu, Jiyan Liu An Alternating current (AC) electrical field was applied to induce the movement of the clay nanoparticles in polydimethylsiloxane (PDMS) to fabricate flexible membranes embedded with thickness-direction aligned nanoparticles. The influence of the electric field strength and frequency on the movement of the particles in the PDMS monomer was investigated using an optical microscope. The morphology of the aligned clay/PDMS membranes frozen with thermal curing was analyzed with scanning electron microscopy (SEM) and confocal Raman spectroscopy. Benefiting from the anisotropic structure of aligned particle chains, the aligned clay/PDMS membranes show enhanced mechanical properties, thermal conductivity, and the light transmittance in the thickness direction compared to nonaligned membranes. This enhancement effect decreases as the particle concentration exceeds 5 wt %. The reason is that at higher clay concentrations, alignment of the particle is frustrated and particle chains become tilted and irregular owing to an increment in the viscosity of the system.
       
  • Fabrication of a piezoelectric polyvinylidene fluoride/carbonyl iron
           (PVDF/CI) magnetic composite film towards the magnetic field and
           deformation bi-sensor
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Min Sang, Sheng Wang, Mei Liu, Linfeng Bai, Wanquan Jiang, Shouhu Xuan, Xinglong Gong In this paper, a versatile polyvinylidene fluoride/carbonyl iron (PVDF/CI) composite film was prepared by doping magnetic carbonyl iron (CI) particles into piezoelectric polyvinylidene fluoride (PVDF) matrix. Without influencing the piezoelectric structure of PVDF, CI particles enhanced the Young's modulus and maximum tensile strength of composite films. Due to the magnetic driven characteristic, PVDF/CI composite films exhibited distinct magnetic-mechanic-electric coupling properties. The piezoelectric charge signals could be generated by applying the bending deformation or magnetic field. Taking PVDF/CI-10% (CI content was 10 wt%) film as an example, the piezoelectric charges under 2, 4, 6, 8, and 10 mm bending displacement were 3.0, 9.6, 14.9, 18.6, and 24.6 pC respectively. Moreover, when the magnetic field varied from 0 to 600 mT, the generated magneto-electric charges of PVDF/CI-10% film increased from 0 to 676 pC. The quantitative relationship between magnetic field and magneto-electric charges was obtained by the polynomial fitting method and the correlation coefficient was up to 0.97. Owing to the ideal piezoelectricity, excellent stability, light weight and desirable flexibility, PVDF/CI composite films showed promising applications in deformation sensor and magnetic field sensor.
       
  • Exchangeable interfacial crosslinks towards mechanically robust
           elastomer/carbon nanotubes vitrimers
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Min Qiu, Siwu Wu, Zhenghai Tang, Baochun Guo Covalent bonds mediated interfaces are generally favorable for transferring interfacial stress and hence rationalizing the mechanical properties of the filled elastomeric composites. Aiming at reprocessable yet robust elastomeric composites, in this contribution, exchangeable interfacial crosslinks are introduced into the interfaces between epoxidized natural rubber (ENR) and multi-walled carbon nanotubes (MWCNTs). This is accomplished by functionalizing MWCNTs with carboxyl groups through diazo-coupling reaction and then incorporating the modified MWCNTs into diacid-cured ENR. Accordingly, covalent β-hydroxy ester bonds result in the interfaces between ENR and MWCNTs. The formation of covalent interfaces enables much uniform dispersion of MWCNTs and stronger interfacial adhesion. Comparing to the ENR filled with pristine MWCNTs, the modified composites exhibit much improved mechanical performance. Importantly, the exchangeable nature of interfacial β-hydroxy ester bonds has promoted effect on the reprocessibility of epoxy-MWCNTs vitrimers. Overall, we envision this interfacial strategy can provide an alternative avenue towards reprocessable yet robust elastomeric composites.
       
  • Uniformly dispersed polymeric nanofiber composites by electrospinning:
           Poly(vinyl alcohol) nanofibers/polydimethylsiloxane composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kentaro Watanabe, Tomoki Maeda, Atsushi Hotta A method for the fabrication of homogeneous and well-dispersed polymeric nanofiber composites was investigated. Nanofiber fillers can be used to produce polymeric nanocomposites by mixing the fillers to base polymers, eventually enhancing the mechanical property of the matrix polymers. To produce such composites, nanofibers were usually sandwiched by molten matrix polymers at high temperature before molding. The traditional so-called sandwich method, however, was found to produce rather biased and inhomogeneous composites due largely to the solid entanglement of the nanofibers. In this work, unwoven polymer nanofibers were synthesized through electrospinning by controlling the electrostatic repulsion of the nanofibers. We modified the electrospinning apparatus for the direct synthesis of homogenous composites: nanofibers were electrospun and directly ejected from the electrospinning syringe to the matrix polymer solution (not in a solid state), where a regular metal electrode plate was replaced by an optimized metal container containing the base polymer solution. It was found that this new fabrication method could realize homogeneous mixing of the nanofibers that were eventually uniformly dispersed in the polymer solution. Poly(vinyl alcohol) (PVA) was used for nanofibers and polydimethylsiloxane (PDMS) was used for polymer matrix. The field emission scanning electron microscopy (FE-SEM) revealed the homogeneous and well-dispersed PVA nanofibers in the resulting PDMS composites. The composites also presented higher mechanical properties as compared with the composites fabricated by the traditional sandwich method.
       
  • Nanodiamond decorated graphene oxide and the reinforcement to epoxy
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Weixin Hou, Ya Gao, John Wang, Daniel John Blackwood, Serena Teo Positively charged nanodiamond (ND) is used to decorate negatively charged graphene oxide (GO) to form a GO-ND hybrid nanomaterial by electrostatic force. Structural studies results showed that after the decoration, the aggregation of GO sheets is extensively hindered in both at the powder and dispersion states, with a clear reduction in the layer numbers in the latter. The mechanical properties of epoxy/GO, epoxy/ND and epoxy/GO-ND were investigated and compared. The results showed that the GO increased the ductility of epoxy, while the ND increased the rigidity. The best mechanical performance was found for the epoxy/GO-ND nanocomposites, at a GO:ND ratio of 1:5. The reinforcement mechanism of the nanophases was further illustrated by the fracture surface of SEM/optical images and TGA analysis. In addition, the anti-corrosion property of the thus developed epoxy nanocomposite coatings was revealed by electrochemical impedance spectroscopy (EIS), and the results demonstrated that the epoxy/GO-ND coatings exhibited better anti-corrosion property.
       
  • The effect of polymer particle size on three-dimensional percolation in
           core-shell networks of PMMA/MWCNTs nanocomposites: Properties and
           mathematical percolation model
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Seung Han Ryu, Hong-Baek Cho, Seil Kim, Young-Tae Kwon, Jimin Lee, Kee-Ryung Park, Yong-Ho Choa Segregated highly conductive percolation networks in nanocomposites consisting of a polymethyl methacrylate (PMMA) core and multi-walled carbon nanotube (MWCNT)-shell were investigated experimentally as a means of exploring the relationship between the micro-dimensional size of spherical polymer particles and the number of coated MWCNT layers by a new theoretical approach of filler monolayer model. The measured electrical conductivity of the core-shell structured complex utilizing 20 μm PMMA spheres showed that percolation was achieved at a very low filler content of 0.0099 wt% MWCNTs, whereas 0.149 wt% MWCNT was required to achieve percolation when 5 μm PMMA spheres were utilized. The size of PMMA cores was attributed to the percolation threshold, and conductivity was enhanced by increased layers of MWCNT coating. The percolation behaviors based on the theoretical model and experimental data were elucidated. Furthermore, an advanced theoretical model for prediction of number of MWCNT monolayers was provided.
       
  • Covalent functionalization of carbon nanotubes with hydroxyl-terminated
           polydimethylsiloxane to enhance filler dispersion, interfacial adhesion
           and performance of poly(methylphenylsiloxane) composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Lu Bai, Zhongxiao Li, Shizhen Zhao, Junping Zheng Surface modification of carbon nanotubes (CNTs) were performed by grafting of hydroxyl-terminated polydimethylsiloxane (HPDMS) covalently. The results of dissolution experiments revealed that long-time stable dispersions of HPDMS-functionalized CNTs (CNTs-HPDMS) were achieved in a range of solvents including ethanol, ethyl acetate, dimethylbenzene and cyclohexane, even after being placed for 3 months. Subsequently, CNTs-HPDMS were incorporated into poly(methylphenylsiloxane) (PMPS) matrix to prepare composites. Scanning electron microscopy analysis showed that CNTs-HPDMS had homogeneous dispersion and strong interfacial adhesion in PMPS, which led to much better mechanical properties of composites compared to those filled with untreated CNTs. Furthermore, the incorporation of CNTs-HPDMS significantly enhanced the thermal stability of PMPS composites both under nitrogen and air. The improved barrier effect of CNTs-HPDMS resulted from the better filler dispersion was considered to play a crucial role, which on the one hand suppressed the depolymerization of PMPS under nitrogen and on the other hand inhibited the oxygen diffusion in matrix under air. Besides, the hydroxyl groups of HPDMS could react with PMPS to form additional crosslinking during heating, and thus delayed the degradation of PMPS to some extent.
       
  • 3D-printed PEEK-carbon fiber (CF) composites: Structure and thermal
           properties
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): А.А. Stepashkin, D.I. Chukov, F.S. Senatov, A.I. Salimon, A.M. Korsunsky, S.D. Kaloshkin CF-PEEK composites were manufactured by 3D-printing using a novel FDM methodology and customized printer and were compared with their cast counterparts. The characterization of composite thermal properties in the range 25–300 °C revealed that 3D-printed CF-PEEK composites manifest 25–30% lower thermal conductivity than cast composites. Short carbon fibers used for reinforcement showed orientation along the polymer flow both in cast and 3-D printed samples causing the anisotropy of thermal properties. The hierarchical nature of 3DP CF-PEEK porosity was observed by SEM imaging, which allowed the identification of large scale inter-layer gaps and cracks, and fine scale intra-layer defects that are likely to be induced by the thermal and mechanical gradients within the deposit that arise during fabrication. Purposeful lay-up of long continuous carbon yarns during 3D-printing opens a way to fabricate tailored mechanical parts with desired anisotropy of properties.
       
  • Enhancement of mechanical properties of buckypapers/polyethylene
           composites by microwave irradiation
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Bo Qu, Dongxian Zhuo, Rui Wang, Lixin Wu, Xiuyan Cheng Buckypapers (BPs) were generally laid up interleaved with polyethylene (PE) films to form BPs/PE composites after hot press. However, the mechanical properties of BPs/PE composites as-prepared were not good enough owing to poor impregnation and weak interfacial interactions between the matrix and carbon nanotube (CNT). In this paper, controlled microwave radiation treatment was applied on the BPs/PE composites. It is found that the microwave irradiation can effectively improve the tensile strength and stiffness of BPs/PE composites. Specifically, the tensile strength of BPs/PE composites increases from 20.9 MPa upto 34.1 MPa, 2.8 times that of pure PE, while the modulus increases from 880 MPa to 1778 MPa, 3.0 times that of pure PE. In addition, the structures (including fractured morphology, the interfacial composition between CNT and PE, structure of CNT and PE matrix, and crystallization) of BPs/PE nanocomposites with and without microwave irradiation were observed by SEM, FTIR, Raman, X-ray, and DSC, and then a mechanism of microwave irradiation to enhance the mechanical properties of BPs/PE composites was also proposed.
       
  • Electrically conductive GNP/epoxy composites for out-of-autoclave
           thermoset curing through Joule heating
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Tian Xia, Desen Zeng, Zheling Li, Robert J. Young, Cristina Vallés, Ian A. Kinloch The development of scalable Out-of-Autoclave (OoA) in-situ thermoset curing methods are required to overcome important drawbacks related to the autoclave-based processing methods typically used in industry. The incorporation of graphene, an electrothermal carbon nanomaterial with the ability to transform electric energy into heat through Joule heating, emerges as a promising route to replace the conventional processing methods. In this work the electrical behaviour of both uncured and oven cured GNPs/epoxy composites with loadings of up to 10 wt% were evaluated and electrical percolation thresholds were established for both. Above the critical loading found for oven cured materials (∼8.5 wt%) the electrically conducting networks of GNPs formed in the matrix showed the ability to act as integrated nanoheaters when an electric current was passed through them, successfully curing the composites by Joule heating. Composites prepared by this OoA curing method (as an alternative to the traditional oven based one) at 10 wt% loading of GNPs were also prepared and compared to the oven cured ones. They showed more compact composite structures, with less microvoids and a preferred orientation of the GNPs in the matrix relative to the oven cured material at identical loading, as revealed by electron microscopy and polarized Raman spectroscopy, respectively. This microstructure and anisotropy induced by the electrically-induced (i.e. OoA) cure led to GNPs/epoxy composites with superior electrical and mechanical properties (revealed by tensile testing). The well-distributed GNP nanoparticles acting as nanoheaters integrated in a thermosetting matrix, in combination with excellent mechanical and electrical performances achieved for the overall graphene/epoxy composites and the simplicity associated to the method, should open the door to novel industrial applications.
       
  • Transparent plywood as a load-bearing and luminescent biocomposite
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Qiliang Fu, Min Yan, Erik Jungstedt, Xuan Yang, Yuanyuan Li, Lars A. Berglund Transparent wood (TW) structures in research studies were either thin and highly anisotropic or thick and isotropic but weak. Here, transparent plywood (TPW) laminates are investigated as load-bearing biocomposites with tunable mechanical and optical performances. Structure-property relationships are analyzed. The plies of TPW were laminated with controlled fiber directions and predetermined stacking sequence in order to control the directional dependence of modulus and strength, which would give improved properties in the weakest direction. Also, the angular dependent light scattering intensities were investigated and showed more uniform distribution. Luminescent TPW was prepared by incorporation of quantum dots (QDs) for potential lighting applications. TPW can be designed for large-scale use where multiaxial load-bearing performance is combined with new optical functionalities.Graphical abstractTransparent plywood (TPW) is obtained by laminated veneers with tunable orientations, resulting in significant improvement of mechanical and optical properties. A UV sensitive luminescent TPW is demonstrated by incorporation of TPW with CdSe/ZnS quantum dots (QD). This material may broaden wood nanotechnology for applications in building materials, optical and photonic devices.Image 1
       
  • Strengthening carbon nanotube fibers with semi-crystallized polyvinyl
           alcohol and hot-stretching
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Jialin Liu, Wenbin Gong, Yagang Yao, Qingwen Li, Jin Jiang, Yong Wang, Gengheng Zhou, Shuxuan Qu, Weibang Lu The tensile mechanical properties of carbon nanotube (CNT) fiber, which is a one-dimensional assembly of ultra-strong CNTs, are still far short of our expectations. This is mainly due to their high porosity and relatively weak intertube load transfer efficiency. Previous studies have demonstrated that the fiber strength can be enhanced by the infiltration of polymer chains into the fiber. In this work, polyvinyl alcohol (PVA) was pre-infiltrated into loosely packed CNT ribbons, and the composite ribbons were then densified into the fiber form. This enabled a homogeneous dispersion of polymer chains within the CNT fibers. To enhance the mechanical properties of the CNT/PVA composite fibers, isothermal crystallization and ultrasonic treatments were implemented to increase the crystallization of PVA in the ribbon, and the composite fibers were hot-stretched to improve the alignment of both CNTs and PVA chains within the fibers. It was found that the tensile strength and modulus of the final composite fiber were 210% and 193.6% higher than those of the pristine CNT fiber. The structural evolution during these treatments and the mechanism of fiber strengthening were systematically investigated.
       
  • Pressure-crystallized piezopolymer/ionomer/graphene quantum dot
           composites: A novel poling-free dynamic hybrid electret with enhanced
           energy harvesting properties
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Chenwen Xu, Long Jin, Lei Zhang, Chuanfeng Wang, Xi Huang, Xuebing He, Yali Xu, Rui Huang, Chaoliang Zhang, Weiqing Yang, Jun Lu We report the design and fabrication of a novel self-powered poling-free dynamic electret by hybridizing a piezocomposite with graphene quantum dots (GQDs). The polymeric hybrid piezoelectret was prepared through the solution casting of a ternary poly (vinylidene fluoride) (PVDF)/Nafion/GQD composite followed by pressure crystallization. During the fabrication, Nafion ionomer filled PVDF cells, resulting in the formation of artificial macroscopic dipoles, and GQDs induced the self-assembly of macromolecular chains in PVDF cell walls, leading to the growth of piezoelectric nanowires. The synergistic action of the man-made macroscale dipoles of Nafion and the inherent molecular dipoles of PVDF cells, together with the deformation and relaxation of the in situ formed polar crystalline polymeric nanowires, enabled the PVDF/Nafion/GQD composites to convert kinetic mechanical energy into electricity with remarkably enhanced efficiency. Compared with its PVDF/Nafion counterpart, the electrical output of a developed PVDF/Nafion/GQD nanogenerator, without any treatment of electrical poling, achieved considerable increase in both short-circuit current and open-circuit voltage, and showed better stable and durable performance for more than 20000 continuous working cycles. Particularly, the PVDF/Nafion/GQD composite also exhibited more improved mechanical-to-electrical conversion even if it has endured a long-term brine disposal. The study presented herein may open a new avenue for the manufacturing of a new class of electret-transducer materials that permit applications in powering autonomous micro-/nano-systems with high operational and environmental stability.
       
  • Carbon fiber/epoxy matrix composite interphases modified with cellulose
           nanocrystals
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Mariana Desireé Reale Batista, Lawrence T. Drzal Cellulose nanocrystals (CNCs) were used to modify the interphase between carbon fiber (CF) and an epoxy matrix to simultaneously strengthen and toughen the CF composite. CNCs were functionalized with 3-aminopropyltriethoxysilane (APTES) and surface modification was confirmed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), which revealed the presence of the new chemical species. Functionalized CNCs (APTES-CNCs) were applied as part of a sizing to coat CFs and an optimum concentration was identified. Single fiber fragmentation tests (SFFT) showed that stronger adhesion between the CFs and the epoxy matrix was achieved for the fibers sized with APTES-CNCs, compared to unsized CFs and epoxy-only sized CFs. CFs sized with APTES-CNCs at a concentration of 1.0 wt% resulted in 81% increase in interfacial shear strength (IFSS) compared to unsized CFs, and the birefringent stress pattern seen during the SFFT supports the assumption that adding APTES-CNCs at the composite interphase promotes an improvement in the failure mode. These results demonstrate that sizing CFs with APTES-CNCs is an effective method to increase the interfacial properties in CF reinforced epoxy composites, and a potential approach for the development of ecofriendly and lightweight composite materials for aerospace and automotive applications.
       
  • One-pot method to reduce and functionalize graphene oxide via
           vulcanization accelerator for robust elastomer composites with high
           thermal conductivity
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Huanhuan Dong, Zhixin Jia, Yongjun Chen, Yuanfang Luo, Bangchao Zhong, Demin Jia A high-efficiency and rapid one-step approach was developed to simultaneously reduce and functionalize graphene oxide (GO) with vulcanization accelerator 2-mercaptobenzothiazole (M) under mild conditions (2 h, 80 °C, neutral and non-toxic environmental condition). The reduced GO chemically grafted with ca. 25 wt% M (M-G) not only eliminated the harmful blooming of vulcanization accelerator but also reduced the irreversible graphene agglomerates and improved the compatibility between graphene and elastomer, aiding the uniform dispersion of M-G nanosheets in elastomer matrix and enhancing the graphene-elastomer interfacial interaction. As a result, elastomer composites with M-G nanosheets showed much better combination of high tensile strength, large extensibility and superior thermal conductivity than elastomer composites with hydrazine hydrate reduced GO containing equal filler and vulcanization accelerator contents. The approach of using rubber additives to reduce and functionalize GO may provide some new insights in the green production of organically modified graphene and in the designing of high performance rubber/graphene materials.
       
  • Effect of PA6T on morphology and electrical conductivity in
           PA66/PA6T/PPE/multiwalled carbon nanotube nanocomposites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Minho Lee, Kwonsang Son, Jeongyup Kim, Donghyeon Kim, Byong Hun Min, Jeong Ho Kim Nanocomposites made of blends of polyamide (PA66), polyphthalamide (PA6T), and poly(2,6-dimethyl-1,4-phenylene ether) (PPE) with multi-walled carbon nanotubes (CNTs) were investigated. At 1 wt% CNT loading, the electrical conductivities of PA66/PA6T/PPE/CNT nanocomposites were around four orders of magnitude larger than those of PA66/PPE/CNT nanocomposites without PA6T. Line mapping images and spot spectrum results from transmission electron microscopy/energy dispersive spectroscopy analysis showed that the continuous phase contained PA66 and PA6T with dispersed PPE domains. Phase inversion was observed as the CNT content of PA6T/PPE/CNT increased. Depending on the polymer composition, alignment of some of CNTs at the interface was observed. Using the wetting coefficient analysis and the Hansen solubility parameter, the morphologies of the nanocomposites and the resulting electrical conductivities were found to be affected by the compatibilizing effect of PA6T on PA66 and PPE as well as the higher affinity of CNTs for PA6T than for PPE or PA66. CNTs were observed to help maintain the integrity of the PA66/PA6T continuous phase by dynamic mechanical analysis.
       
  • Exploiting cyclic softening in continuous lattice fabrication for the
           additive manufacturing of high performance fibre-reinforced thermoplastic
           composite materials
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Martin Eichenhofer, Joanna C.H. Wong, Paolo Ermanni Continuous lattice fabrication (CLF) was recently introduced as a new additive manufacturing (AM) technology capable of printing continuous fibre-reinforced thermoplastic composites along desired trajectories in three-dimensional space. In a systematic attempt to maximize the mechanical properties of the printed extrudate by minimizing the residual void content, this study investigates the thermal deconsolidation behaviour observed in pultruded unidirectional fibre-reinforced thermoplastic composite material when it is reheated above its melting point and exposed to ambient pressure. Fibre decompaction, generally accepted to be the primary cause for deconsolidation in fibre-reinforced thermoplastics, was investigated to assess the influence of cyclic softening of the fibrous media on the residual void content of the extruded material. The magnitude and rate of fibre decompaction were observed to decrease with the number of consolidation-deconsolidation cycles to which the material was subjected. A model was developed to predict the degree of deconsolidation in the CLF process as a function of temperature, processing speed, and processing history. Based on the deconsolidation behaviour observed, a multi-stage pultrusion module was designed that exploits cyclic softening and was demonstrated to reduce the residual void content of the printed extrudate by over 80%.
       
  • Fabrication of a bulk superhydrophobic conductive material by mechanical
           abrasion
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Zhiming Cai, Lie Shen, Xiaojing Wang, Qipeng Guo A Ketjen black (KB)-vapour-grown carbon fibre (VGCF)/polypropylene (PP) bulk superhydrophobic conductive material was prepared by processing the mixture with a range of roughnesses of abrasive paper. The difference in abrasion resistance between fillers and resin induces surface roughness during abrasion. SEM images showed hierarchically structured roughness that consists of heaves with fillers. The influence of the loading and ratio of the fillers was investigated. When the loading of the fillers was 33.3 wt% and the ratio of KB to VGCF was 4:1, the surface showed a static water contact angle of approximately 167.5°, a sliding angle below 1°, and a volume resistivity of approximately 0.8 Ω cm. The superhydrophobicity of the material was stable over a wide range of pH, temperature and appropriate mechanical abrasion. The bulk material is environmentally friendly, easy to scale up for large-scale applications and may be useful for anti-icing applications or self-cleaning.
       
  • Effect of tunable styrene content on achieving high-performance
           poly(styrene-b-ethylene-ran-butylene-b-styrene)/graphene oxide
           nanocomposites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Jianfeng Wang, Xiuxiu Jin, Xiaomeng Zhang, Hong Wu, Shaoyun Guo In this paper, two poly(styrene-b-ethylene-ran-butylene-b-styrene) (SEBS) with different styrene segment content were adopted to explore the relationship between varying π-π stacking interaction and the mechanical performance of polymer composites. The results showed that the high styrene content on SEBS (SEBS-30, 30 wt% styrene segment) endows SEBS a stronger π-π stacking interaction with GO and a better dispersion of GO in the matrix than that in SEBS with low styrene content (SEBS-12, 12 wt% styrene segment), resulting in a high efficiency on enhancing the performance of SEBS. By adding 0.5 wt% GO, the tensile strength and modulus of SEBS-30 was increased by 44% and 64%, respectively, while that of SEBS-12 was increased by 24% and 39%. Furthermore, the GO also exhibited the ability to toughen SEBS via forming microcrack and GO-induced fibrillation of SEBS during the fracture process. The elongation at break and fracture toughness of SEBS-30 was increased by 10% and 64%, respectively. This study gives us a deep insight into the influence of varying π-π stacking interaction between graphene oxide (GO) and polymer on achieving high-performance polymer nanocomposites.
       
  • Surface modification of carbon fibers by microwave etching for epoxy resin
           composite
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Jian-Min Yuan, Ze-Fu Fan, Qing-Cheng Yang, Wei Li, Zhen-Jun Wu Microwave irradiation was applied to modify the carbon fibers immersed in water. The surface chemical composition and morphology of treated carbon fibers were investigated in detail. It showed that great numbers of oxygen-containing groups were introduced in treated carbon fiber surfaces and nitrogen heterocyclic rings of carbon fiber bulk exposed for the exfoliation of surface layers. The surface roughness of carbon fibers was enlarged by oxidative etching of microplasma excited by microwave irradiation, and some nano humps were formed on carbon fiber surfaces. Although the tensile strength of treated carbon fibers were slightly deteriorated, the interfacial shear strength of treated carbon fibers/epoxy resin composite, as compared with that of untreated carbon fibers/epoxy resin composite, was significantly enhanced. The modification mechanism is that the microplasma and the exfoliation of monolayer graphene oxide sheets lead to the variations of chemical structure and physical morphology in carbon fiber surfaces.
       
  • Enhanced energy storage performance of ferroelectric polymer
           nanocomposites at relatively low electric fields induced by surface
           modified BaTiO3 nanofibers
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Zeyu Li, Feihua Liu, Guang Yang, He Li, Lijie Dong, Chuanxi Xiong, Qing Wang Polymer nanocomposite dielectrics with high energy densities have shown great potential in electrical energy storage applications. However, these high energy densities are normally achieved at ultrahigh applied electric fields (≥400 MV/m), which is inconvenient for certain applications such as aerospace power systems and microelectronics. In this study, uniform BaTiO3 nanofibers (BT nfs) with a large aspect ratio were prepared via the electrospinning method, surface modified by poly(vinyl pyrrolidone) (PVP) and utilized as the fillers in the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) nanocomposites. It is found that the nanocomposite with 3 vol% BT nfs possesses a much enhanced discharged energy density of 8.55 J/cm3 at an applied electric field of 300 MV/m, which is 43% higher than that of the neat polymer matrix (i.e. 5.98 J/cm3) and more than four times that of the commercial biaxial oriented polypropylene dielectric (2 J/cm3 at over 600 MV/m). Comparative studies have been performed on the corresponding nanocomposites with BT nanoparticle fillers and pristine BT nfs. The improved energy storage performance is ascribed to the synergetic effects of surface modification and large aspect ratio of BT nfs. Our research provides a facile and effective approach to high-performance electrical energy storage materials which work efficiently at relatively low operating voltages.
       
  • Imidazolium-grafted graphene oxide via free radical polymerization: An
           efficient and simple method for an interpenetrating polymer network as
           electrolyte membrane
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Amina Ouadah, Tianwei Luo, Jing Wang, Shuitao Gao, Xing Wang, Xin Zhang, Zhou Fang, Zeyu Wu, Jie Wang, Changjin Zhu In this work, graphene oxide (GO) is modified via free radical polymerization with butylvinylimidazolium (b-VIB) to produce GO/IM, which is characterized using FTIR spectral analysis, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman analysis, X-ray photoelectron spectroscopy (XPS), elemental analysis, and a morphology study with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Further, GO/IM is incorporated for an in-situ polymerization, with the synthesized copolymer para-methyl styrene/butylvinylimidazolium (PMS/b-VIB) and synthesized poly(4,4′-diphenyl ether-5,5′-bibenzimidazole) (DPEBI) as a matrix, giving nanocomposite membranes referred to as GO/IM-X. These nanohybrid membranes possess higher conductivity than the pristine membrane of PMS/b-VIB/DPEBI and the conductivity increases with increasing amount of GO/IM, reaching 78.5 mS cm−1 at 100 °C and 26.5 mS cm−1 25 °C (chloride conductivity), enhancements of about 14.93% and 33.16% compared to the pristine membrane. Nanocomposite membrane properties were investigated; the swelling ratio and water uptake, ion exchange capacity (IEC), thermal properties via TGA, structure characterization using FTIR, morphology via TEM and mechanical properties. Taken together, these results suggest the present nanohybrid membranes have great potential for use as polymer electrolyte membranes with fuel cell applications.Graphical abstractImage 1
       
  • Interfacially reinforced unsaturated polyester carbon fiber composites
           with a vinyl ester-carbon nanotubes sizing agent
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Zijian Wu, Hongyu Cui, Lei Chen, Dawei Jiang, Ling Weng, Yingyi Ma, Xuejiao Li, Xiaohong Zhang, Hu Liu, Ning Wang, Jiaoxia Zhang, Yong Ma, Mingyan Zhang, Yudong Huang, Zhanhu Guo A amino-functionalized carbon nanotubes (CNTs)-containing sizing agent was prepared for improving the interface bonding and impact toughness of carbon fibers (CFs) reinforced unsaturated polyester (UP) composites. More reactive groups and better interfacial compatibility with UP make vinyl resin M7270 a more suitable polymer for preparing sizing agent for CF/UP composites when compared to epoxy, MR13006 and R806. The surface characteristics of CFs and the interfacial properties of the composites before and after surface modification were investigated. The observed uniformly dispersed CNTs-containing sizing agent on the CF surface obviously increased the surface roughness. The amount of polar functional groups and the wettability of CFs were significantly enhanced after the coating treatment. The interlaminar shear strength (ILSS) and impact toughness were enhanced by 32.3 and 55.2%, respectively. The sizing agent effectively enhanced the interfacial adhesion by improving the surface energy, and increasing chemical bonding and mechanical interlocking.
       
  • Flexible, conductive, and highly pressure-sensitive graphene-polyimide
           foam for pressure sensor application
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Jiayi Yang, Yusheng Ye, Xiaoping Li, Xiaozhou Lü, Renjie Chen Three-dimensional porous graphene foams have received increasing attention in the fields of sensors, flexible conductors, and energy storage. Mechanical stability, flexibility, and electrical conductivity are prerequisites for materials used in these fields. In this paper, novel polyimide-based graphene foam was prepared by dip-coating a polyimide foam template followed by chemical reduction and thermal reduction. The prepared foam displayed excellent mechanical stability and flexibility (elastic modulus: ∼5 kPa). The synergistic effects of chemical and thermal reduction led to a foam with high electrical conductivity of ∼0.4 S m−1. By controlling the dip-coating times, the foam achieved a high pressure sensitivity of 0.36 kPa−1. Experiments show that the prepared foam can be used as effective pressure sensor to measure heartbeat, joint activity, and airflow.
       
  • A three-dimensional unit cell model with controllable crimped structure
           for investigating finite strain response of collagen fiber reinforced
           biological composites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Li Liu, Dean Hu, Xu Han Composite materials reinforced by crimped fibers, such as collagen fibers, have a widely application in the advanced structures. Therefore, an effective and achievable model is significant for explicitly describing the geometry of the crimped fibers and evaluating their mechanical behaviors. Aiming at this purpose, a three-dimensional (3D) unit cell model (UCM) is developed based on the microstructure of the collagen fibers, in which a controllable modified sinusoidal waviness fiber is explicitly embedded into the soft matrix, and an effective periodic boundary condition is applied on the proposed 3D UCM by using the multi-points constraint equations. The accuracy and validity of the proposed model are verified by comparing with the existing experimental results. For investigating the influence of the geometric parameters on the mechanical responses of the crimped fiber reinforced composites, several numerical UCMs with different geometric parameters are presented. The obtained results reveal that the parameters of crimp amplitude H and waviness χ of the fibers mainly contribute to the flexibility of the materials. The parameter ω for characterizing the roughness of the fibers is associated with the size and position of largest stress region. Moreover, the fiber radius R plays an important role in determining the bearing capacity of the materials and an excellent mechanical property, e.g., not only withstands the large initial tensile load but also has a special ability to guarantee the flexibility of the materials, may be achieved by controlling the number of the fibers with big and small radii.
       
  • Core-shell nanoparticles toughened polylactide with excellent transparency
           and stiffness-toughness balance
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Yuan Chen, Mingwang Pan, Yue Li, Jia-Zhuang Xu, Gan-Ji Zhong, Xu Ji, Zheng Yan, Zhong-Ming Li Polylactide has attracted increasing focus on packaging and other consumer products nowadays, due to its stiffness, biodegradability and good transparency. However, its toughened blends are usually utilized to conquer its inherent brittleness, unfortunately, bringing with undesirable opaqueness. Considering the transparency and toughness of PLA, nanoparticles with core-shell structure, which are one kind of methyl methacrylate–butyl acrylate (ACR) copolymers whose rubbery cores resist impact and the glassy shells provide rigidity and compatibility to the polymer matrix, were manipulated by seed emulsion polymerization in this work, aiming to toughen PLA without the substantial decrease of transparency and tensile strength simultaneously. The effects of size and content of ACR nanoparticles on the optical properties, mechanical properties of PLA/ACR blends respectively were clarified. The PLA/ACR blends exhibited excellent transparent property with a transmittance as high as 75% (550 nm). We found an unexpected relationship between particles size and transparency, that is, with the decrease of ACR size, the transparency of blends was also reduced slightly. This phenomenon may contribute to the scattering of bigger aggregation formed by ACR with smaller size, which was identified by microstructure observations. Tensile testing showed the maximum elongation at break of 279.9% when ACR content reached 20 wt%, which was a 65-fold increase compared with neat PLA. Promisingly, the elastic modulus and tensile strength exhibited less decreased with the value of 55.7 MPa and 2.06 GPa respectively, and this blends displayed 8 times the Izod impact strength over neat PLA. It was revealed the shear yielding of matrix and cavitation of particles during the loading process led to the excellent toughness of PLA/ACR blends.Graphical abstractImage 1
       
  • Effect of hierarchical structure on electrical properties and percolation
           behavior of multiscale composites modified by carbon nanotube coating
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Jie Zhang, Alexei A. Bokov, Shang-Lin Gao, Nan Zhang, Jian Zhuang, Wei Ren, Zuo-Guang Ye The hierarchical composites integrated by micro-/nano-fillers have been considered to be the multifunctional materials of the next generation. However, the effects of the hierarchical architecture on the electrical properties of composites remains poorly understood. Here, the fabrication of polymer-based multiscale composites with hollow glass fibers coated by carbon nanotubes (CNTs) and the investigation of their morphology, conductivity and dielectric properties are reported. Owing to CNTs introduced into the interfaces, various electrical parameters of the composites are obviously improved. The composite exhibits a stronger anisotropy than that of carbon fiber or CNTs filled composites and an ultralow percolation threshold. These unique behaviors are shown to be related to the hierarchical morphology giving rise to the existence of two percolation levels with different thresholds: a local threshold in the nanoscale CNT networks at the fiber-polymer interfaces and a global threshold in 3D network formed by the fibers. Furthermore, we find and explain some behaviors uncharacteristic of binary composites and the other hierarchical composites. This work provides a deeper understanding of the relationship between the structure and properties of multiscale composites and other complex percolating systems, potentially opening up new ways for designing novel materials.
       
  • Highly thermal conductive and electrically insulating polymer composites
           based on polydopamine-coated copper nanowire
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Hao Yuan, Yang Wang, Ting Li, Piming Ma, Shengwen Zhang, Mingliang Du, Mingqing Chen, Weifu Dong, Weihua Ming Thermally conductive but electrically insulating polymer composites are highly desired for thermal management applications because of their ease of processing, light weight, and low cost. Copper nanowires (CuNWs), due to their inherent thermal conductivity and high aspect ratio, hold great potential in thermal management applications. However, CuNW-based polymer composites usually suffer from the deterioration of electrical insulating property. Therefore, it is critically required to reduce significantly the electrical conductivity of CuNW-based composites. In this study, highly thermally conductive but electrically insulating epoxy nanocomposites were prepared by incorporating polydopamine-coated CuNWs. At the volume fraction of 3.1% of CuNW, the thermal conductivity of the nanocomposites reached 2.87 W m-1 K-1, 14 times higher than pristine epoxy, while the electric resistivity remained to be greater than 1014 Ω cm. These highly thermal conductive and electrically insulating nanocomposites are promising for applications in thermal management.Graphical abstractImage 1
       
  • Largely enhanced fracture toughness of the PP/EPDM blends induced by
           adding carbon nanofibers
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): De-xiang Sun, Chao-jin Yang, Xiao-dong Qi, Jing-hui Yang, Yong Wang In this work, a small quantity of carbon nanofibers (CNFs) were incorporated into polypropylene/ethylene-propylene-diene terpolymer (PP/EPDM) blends. The effects of CNF content on the processing flowability, the microstructure of PP matrix and the morphology of elastomer particles were investigated. The results showed that the processing flowability of the material was not apparently influenced. The straight CNFs selectively located in the PP matrix and exhibited oriented dispersion along the flow direction of melt during the injection molding processing. CNFs exhibited nucleation effect on crystallization of PP. Homogeneous EPDM particles with smaller particle diameters were obtained in the blend composites. Mechanical properties measurements showed that the largely enhanced fracture toughness was achieved for the blend composites and the brittle-ductile transition was induced at lower EPDM content. Specifically, incorporating only 0.2 wt% CNFs into the PP/EPDM (85/15), the impact strength was enhanced about 246%. Further results showed that for the blend which exhibited brittle-fracture feature, the brittle-ductile transition could also be induced with increasing CNF content. The toughening mechanisms were then proposed.
       
  • A novel hierarchical thermoplastic composite honeycomb cylindrical
           structure: Fabrication and axial compressive properties
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Bing Du, Liming Chen, Wenjun Wu, Houchang Liu, Yang Zhao, Shiwei Peng, Yongguang Guo, Hao Zhou, Liliang Chen, Weiguo Li, Daining Fang Thermoplastic composite structures are being widely investigated due to their excellent properties such as recycling feasibility and high damage tolerance to meet the increasing demand for lightweight engineering components. A novel hierarchical thermoplastic composite honeycomb cylindrical structures (HTCHCS) with recyclability were designed and fabricated using interlocking assembly technique. The quasi-static axial compression tests were conducted to investigate the mechanical response and energy absorption of HTCHCS. The structural crushing force efficiency can be risen from 0.4 to 0.7 after optimizing the placement mode of axial ribs. The deformation of HTCHCS were experimentally studied and typical deformation modes were obtained. Different from the layer-by-layer collapse for HTCHCS with regular ribs, HTCHCS with staggered ribs showed negative Poisson’ ratio deformation. After large imposed crushing displacement (at least 90%), excellent deformation recovery over 80% initial height was found and reloading carrying and energy absorption abilities can reach to 13% and 12% of initial ones respectively.
       
  • Enhancement in thermal conductivity of polymer composites using aligned
           diamonds coated with superparamagnetic magnetite
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Mingqi Sun, Bing Dai, Kang Liu, Kaili Yao, Jiwen Zhao, Zhijun Lyu, Peng Wang, Yujie Ding, Lei Yang, Jiecai Han, Jiaqi Zhu We report magnetic alignment of single-crystalline microdiamonds with aid of superparamagnetic magnetite in polymeric composites and their material properties. The silicone composite containing aligned microdiamonds shows interesting properties in alignment direction, including enhancement of thermal conductivity, 250% higher than that of randomly dispersed counterpart at a low loading of 5.1 vol%. Composites with aligned diamond exhibited enhanced thermal conductivity and electrical insulation compared with matrix, and are attractive for application as thermal interface materials in the semiconductor industry, though the introduction of magnetite had part of negative effect on electrical resistivity of composites. A two-level model that accounts first-order interaction between particles to calculate effective thermal conductivity of composites with aligned microdiamonds, is found to fit accurately absolute value and tendency of thermal conductivity for composites with aligned particles. Utilizing the modelling procedure, the volume fraction of microdiamonds within chains is 0.3, which is smaller than 0.698 predicted for ideal body-centered-tetragonal arrangement of particles. This suggested that thermal conductivity of composites can be enhanced further by improving microstructures within particle chains.
       
  • Synthesis of novel multilayer composite microcapsules and their
           application in self-lubricating polymer composites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Haiyan Li, Yingjie Ma, Zhike Li, Yexiang Cui, Huaiyuan Wang Novel lubricant oil-loaded multilayer composite microcapsules with poly(urea-formaldehyde) (PUF) shells assembled with polydopamine-functionalized oxidized carbon nanotubes (CNTs-o-PDA) are fabricated. Results indicate that the PUF microcapsules show spherical shape structure with a mean diameter of 110 μm and an encapsulation capacity of 83.5%. CNTs are successfully assembled on the surface of lubricant oil-containing PUF microcapsules (LPMs). Thermal stability tests reveal the initial decomposition temperature of microcapsules elevated by 75 °C. Furthermore, the microcapsules are embedded into epoxy to prepare self-lubricating composites. The coefficient friction and wear rate of self-lubricating composites incorporating 20 wt% CNTs-o-PDA assembled LPMs are 33.79% and 74.28% lower than that of composites incorporating LPMs, and which are 64.07% and 99.54% lower than that of the pure epoxy resin, respectively. Further studies confirm that the interface bonding strength between epoxy and microcapsules is effectively improved by the introduction of CNTs-o-PDA on the surface of PUF microcapsules. The synergistic effect between microcapsules containing lubricant oil and CNT layer played an important role in improving the tribological properties of polymer composites.
       
  • Determination of the strain-energy release rate of a composite laminate
           under high-rate tensile deformation in fibre direction
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Justus Hoffmann, Hao Cui, Nik Petrinic In order to successfully model design-critical impact loading events on laminated composite structures, the rate-dependency of the composite material has to be correctly reflected. In this context, the rate-dependency of the strain-energy release rate for fibre tensile failure under high-rate loading conditions has not yet been satisfyingly explored. This study employed compact tension specimens consisting of IM7/8552 for dynamic testing on a split-Hopkinson tension bar system. Data reduction was based on the area method. The obtained strain-energy release rate for testing under high-rate conditions was determined to GIc,dynf+=82.0±20.8kJ/m2, exhibiting a salient drop compared to its counterpart obtained under quasi-static loading (GIc,QSf+=195.8±18.0kJ/m2). Analysis of the strain field surrounding the crack tip using digital image correlation (DIC) suggested a more extensive damage zone for testing under quasi-static than for high-rate loading. A fractographic analysis of the specimens did not indicate any pronounced difference in terms of fracture surface morphology across the two loading rate regimes.
       
  • Mechanical properties of polypropylene by diversely compatibilizing with
           titanate whiskers in composites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Xuechun Wang, Renfeng Song, Yinjie Chen, Yunhui Zhao, Kongying Zhu, Xiaoyan Yuan Isotactic polypropylene (PP)/titanate whisker composites were tailored by two component blends, in which PP and the titanate fillers were processed with maleic anhydride-grafted polypropylene (PP-g-MAH) and maleic anhydride-grafted polyethylene (PE-g-MAH) as compatibilizing agents, respectively. The whiskers modified with silica and 3-aminopropyl triethoxysilane ensured the hybrid interfacial conceivement, and the usages of the diverse compatibilizers were intended for toughening effect and balanced mechanical properties of PP. Positively compatible PP-g-MAH and anti-compatible PE-g-MAH endowed the composites of PP/titanate whiskers with remarkable rise in notch impact strength of 7.4 ± 0.1 kJ/m2, which was significantly higher than 3.1 ± 0.4 kJ/m2 for PP with trivial deterioration to both tensile and flexural strengths. Differential scanning calorimetry results demonstrated the presence of β-form crystals in the composite, favoring the extra improvement of impact toughness. Variations of glass transition temperature and storage energy detected by dynamic mechanical analysis also revealed both of the compatibilizing agents worked in the composites for reinforcement. With the greatly improved tenacity as well as balanced tensile and flexural properties in the composite, PP could find its potentials as impact plastic materials.
       
  • Fabrication and mechanical properties of CFRP composite three-dimensional
           double-arrow-head auxetic structures
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Xin-Tao Wang, Bing Wang, Zhi-Hui Wen, Li Ma In recent years, 3D structures with negative Poisson's ratio (auxetic) have attracted great interest. Many polymer and metal 3D auxetic structures have been manufactured using additive manufacturing technology, however composite 3D auxetic structures are rarely reported. Auxetic structures are normally of low stiffness which causes limitations on the structural applications of them. The specific stiffness and strength of auxetic structures can be significantly improved by making them from high-performance fibre reinforced polymer (FRP) composites. Consequently, research of composite 3D auxetic structures made from FRP should be conducted. This paper presents the composite 3D double-arrow-head (DAH) auxetic structure made from carbon fibre reinforced polymer (CFRP) using an assembly method. Experimental, finite element and theoretical methods are adopted to study the mechanical properties of the composite 3D DAH auxetic structures. Results show that the Poisson's ratios and effective compression moduli of the composite 3D DAH auxetic structures vary depending on the compression strain amplitude, and the structures become more auxetic and stiffer with the increase of the compression strain. The specific stiffness of the composite 3D DAH structure is much higher than that of the metal structure. In addition, the dependences of the structure's Poisson's ratio and effective compression modulus on the geometry parameters have also been given. Making auxetic structures from high-performance FRP composites can significantly improve their mechanical properties which will enable them to have a much wider variety of applications.
       
  • A novel stiffener skeleton strategy in catalytic carbonization system with
           enhanced carbon layer structure and improved fire retardancy
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Dongsheng Wang, Xin Wen, Xuecheng Chen, Yunhui Li, Ewa Mijowska, Tao Tang Catalyzing carbonization of polymer itself to form a protective carbonaceous layer has been proven to be an effective way to improve polymer's flame retardancy, but there is still a great challenge to achieve synchronous enhancement in traditional test standards (such as LOI and UL-94 testing). In this study, a stiffener skeleton strategy combined with catalyzing carbonization was proposed to improve the flame retardancy of polycarbonate (PC). The synergistic effect of nanosized carbon black (CB)/Ni2O3 on carbon yield and combustion properties of PC were investigated. An improvement with 31.4% in LOI, V0 in UL-94, and 50% reduction for PHRR in cone calorimeter test was achieved. According to char morphology and structure analysis, the flame retardancy mechanism was attributed to the enhanced barrier effect of carbon layer with interconnected structure and self-supporting capacity, which was promoted by the formation of carbon skeleton framework from PC and the catalytic carbonization from combined catalysts.
       
  • Aging resistant TiO2/silicone rubber composites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Monika Bleszynski, Maciej Kumosa We have recently shown [1,2] that one component room temperature vulcanized (RTV-1) silicone rubbers (SIR) based on polydimethylsiloxane (PDMS) can be rapidly degraded by low voltage (LV) energized aqueous salt solutions by previously unreported aging mechanisms related to the formation of hypochlorous acid in high voltage (HV) transmission line applications. In this study, we are showing how to improve the resistance of the rubbers to extreme environmental aging by embedding TiO2 micro-particles. Molecular dynamics (MD) simulations were conducted to determine the combined effect of TiO2 and different concentrations of hydrophobic PDMS methyl groups on surface hydrophobicity of a TiO2/PDMS composite. In addition, the effects of both TiO2 and silica on the diffusivities of LV aqueous salt components in the PDMS were predicted and related to unique interfacial interactions between the particles and the methyl groups of the PDMS. Rutile TiO2 reoriented methyl groups away from the particles reducing the diffusivities of water and hypochlorous acid. This effect shielded the PDMS network against environmental chain scissions. On the other hand, silica attracted the groups accelerating acid and water migrations and thus enhancing damage to the network. In the experimental part, TiO2/RTV was subjected independently to hypochlorous acid and electrolyzed LV aqueous salt. As expected, TiO2 greatly increased the contact angle, reduced the surface energy and improved the hydrophobicity of the composite, mitigating the negative effect of the reduced concentrations of methyl groups. As a result, aging damage to the rubber was dramatically reduced by about 50% in highly oxidative environments.
       
  • Anti-icing and de-icing coatings based Joule's heating of graphene
           nanoplatelets
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): O. Redondo, S.G. Prolongo, M. Campo, C. Sbarufatti, M. Giglio Epoxy coatings doped with graphene nanoplatelets (GNP) with average thickness close to 200 μm have been manufactured on glass fibre laminate substrate. Their electrical conductivity was close to 0.001–0.01 S/m because the GNP percentages added (8–12 wt% GNP) were higher than the electrical percolation threshold of this GNP/epoxy system. The electrical current increases exponentially with the applied voltage due to the self-heating of the samples. Therefore, these materials don't follow the Ohm's law. Interestingly, the electrical resistance remains constant, or even decreases, at cryogenic temperatures. Self-heating of GNP/epoxy coatings due to Joule's effect was also studied, analysing the effect of the applied voltage. The coating doped with the highest GNP content presented more efficient heating due to its higher electrical conductivity and therefore higher transported electrical current.The application of a relatively high voltage, 750–800 V, induced the self-heating of materials, which was used for anti-icing and de-icing applications. Different thermoelectrical tests at low temperatures, between −10 and −30 °C, have been designed and carried out, confirming the high efficiency of these materials as an anti-icing and de-icing system (ADIS) which required low electrical power, close to 2.5 W, showing a short time to melt the ice and high reproducibility.
       
  • Self-healing, recoverable epoxy elastomers and their composites with
           desirable thermal conductivities by incorporating BN fillers via in-situ
           polymerization
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Xutong Yang, Yongqiang Guo, Xian Luo, Nan Zheng, Tengbo Ma, Jiaojun Tan, Chunmei Li, Qiuyu Zhang, Junwei Gu Thiol-epoxy elastomers were firstly prepared by thiol-epoxide nucleophilic ring-opening reaction, and the micron boron nitride (mBN) fillers were then introduced into the above system via in-situ polymerization, finally to prepare the highly thermally conductive, self-healing and recoverable mBN/thiol-epoxy elastomer composites by hot-pressing method. Results revealed that the thiol-epoxide reaction was highly efficient and stable. The obtained mBN/thiol-epoxy elastomer composite with 60 wt% mBN fillers presented the optimal thermal conductivity (λ of 1.058 W/mK), excellent self-healing effect & efficiency which is achieved via transesterification reaction (Tensile strength after self-healing could maintain at more than 85% compared to that of original composites), wonderful recoverable performance (Tensile strength after post forming could maintain over 70% compared to that of original composites) and good thermal stability (Theat-resistance index, THRI of 149.9 °C). And the improvement in λ value of the mBN/thiol-epoxy elastomer composites was beneficial to the promotion of the self-healing systems relying on thermal response.
       
  • A bioinspired multilayer assembled microcrack architecture nanocomposite
           for highly sensitive strain sensing
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Zhenming Chen, Xuehui Liu, Shuman Wang, Xinxing Zhang, Hongsheng Luo Despite the wide applications of strain sensor in wearable devices and electronic skins, the poor flexibility, low sensitivity and repeatability, as well as the utilization of noxious agents dramatically restrict its large-scale application. Herein, a simple and efficient strategy is demonstrated to fabricate flexible, ultrahigh sensitive and reproducible strain-sensing platforms via an eco-friendly water-based layer-by-layer assembly method. Specifically, renewable and biocompatible cellulose nanocrystals with electronegativity were used as the stabilizer to disperse multiwall carbon nanotubes (MWCNTs), meanwhile chitosan solution with rich positive charges was used as the effective “gluing” to enhance the interaction force between the monolayer MWCNTs. The resulting multilayer cracking-structured nanocomposites exhibited ultrahigh sensitivity with a gauge factor ∼359 and detection limit of ε = 0.5%. The samples maintained similar sensitivity even after 200 cycles of stretching/releasing. The high sensitivity is attributed to the disconnection-reconnection of the bioinspired spider-like microcrack junctions in MWCNTs layer. Moreover, the obtained strain sensor showed the abilities to detect not only large-scale body motions (finger bending) but also small-scale physiological strains induced by minute movements of muscles upon swallowing and smiling. It is promising to integrate this kind of strain sensors with human beings in future wearable devices and electronic skins.
       
  • Synthesis of anhydrous manganese hypophosphite microtubes for simultaneous
           flame retardant and mechanical enhancement on poly(lactic acid)
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Wei Yang, Wen-Jie Yang, Benjamin Tawiah, Yang Zhang, Li-Li Wang, San-E Zhu, Timothy Bo Yuan Chen, Anthony Chun Yin Yuen, Bin Yu, Yun-Feng Liu, Jing-Yu Si, En-Zhu Hu, Hong-Dian Lu, Kun-Hong Hu, Qing Nian Chan, Guan Heng Yeoh In this study, a facile solvothermal approach for preparing anhydrous manganese hypophosphite (A-MnHP) microtubes was demonstrated for the first time by using manganese chloride and hypophosphorous acid in mixed solvents, followed by fabricating A-MnHP-based poly(lactic acid) (PLA) composites via a melt-blending method. Owing to the unique morphology of A-MnHP, the tensile strengths of the PLA composites with 1 wt%, 5 wt% and 10 wt% A-MnHP are approximately 17%, 7% and 3% higher than those of neat PLA, respectively. Compared to neat PLA, PLA composite containing 15 wt% A-MnHP (PLA/A-MnHP15) exhibited lower peak heat release rate (50% reduction), total heat release (13% reduction), peak CO2 and CO productions (50% and 53% reductions), which also passed UL 94 V-2 rating test with high limiting oxygen index (27.5%). The combustion temperature change during the cone calorimeter tests showed that PLA/A-MnHP15 showed the lowest combustion temperature, achieving the best fire safety performance. Residue analysis indicated that the presence of A-MnHP resulted in the formation of continuous and compact char residues composed of aromatic structure and phosphorous-rich inorganic structure, retarding the permeation of heat, oxygen transfer and escape of volatile degradation products.Graphical abstractImage 1
       
  • Compatibilization of multicomponent composites through a transitioning
           phase: Interfacial tensions considerations
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): J.Justin Koh, Xiwen Zhang, Junhua Kong, Chaobin He A novel interfacial compatibilization technique for incompatible polymer blends or composites is proposed, in which a transitioning layer was introduced between the matrix and the dispersed phase of the otherwise incompatible components. The transitioning phase should have good interactions with both the components, resulting in lower interfacial energy between the phases. Theoretically, it is hypothesized that if the sum of the interfacial tension between the transitioning phase and both the components of the composite is smaller than the interfacial tension between the two components, the encapsulation of the dispersed phase by the transitioning phase is spontaneous, which will lead to better interphase interfacial interactions. Since this compatibilizing technique relies purely on judicial selection of a polymer with suitable surface energy as the transitioning layer, no tedious chemical synthetic processes are required. To illustrate the proposed technique, incompatible Poly(lactic acid)/Thermoplastic Starch (PLA/TPS) blend is compatibilized with Poly(butylene succinate) (PBS) as the transitioning layer in this paper. With PBS encapsulating the dispersed TPS phase, PLA/PBS/TPS 60/10/30 wt% demonstrate a better mechanical synergy, with significant improvement in strength, ductility and toughness as compared to PLA/TPS 70/30 wt%. This technique can also be applied to design other multicomponent blends or composites.
       
  • Failure load prediction for fiber-reinforced composites based on acoustic
           emission
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Markus G.R. Sause, Stefan Schmitt, Sinan Kalafat In the design and quality control of fiber-reinforced structures, testing on coupon level and structure level are frequently carried out. In order to accept or reject a final product or material charge, means of quality control are carried out. In safety relevant structures, this is often based on holding a certain proof load. Acoustic emission is already used for the monitoring during proof load testing, but is only used for simple accept/reject diagnosis. For the accepted components typically no assessment is made for the expected residual capacity. We propose an acoustic emission based approach able to perform prediction of the ultimate strength values and to evaluate the materials present stress exposure while being tested. We base our approach on accepted acoustic emission measures, such as the Felicity ratio or the Shelby ratio to assess the structural integrity. Using a combination of an artificial neural network to predict the materials present stress exposure and a simple linear extrapolation we are able to predict the failure strength within the margin of prediction error for all test cases studied. The approach is benchmarked for three types of specimens, systematically changing test volume and load condition. We used tensile tests on fiber-reinforced thermoplastic tape samples, classical tensile test samples and bearing strength samples, all made from the same material.
       
  • Thermal, optical, interfacial and mechanical properties of titanium
           dioxide/shape memory polyurethane nanocomposites
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Shuang Shi, Dongya Shen, Tao Xu, Yuqing Zhang To further understand effects of titanium dioxide (TiO2) nanoparticles on thermal, optical, microstructural, interfacial and mechanical properties of shape memory polyurethane (SMPU), TiO2/SMPU nanocomposites with different TiO2 contents were synthesized. Then various properties of TiO2/SMPU nanocomposites were characterized. Results indicate that the melting temperature of soft segments in SMPU can be used as the shape memory transition temperature of TiO2/SMPU nanocomposites. TiO2 nanoparticles are almost filled in SMPU pores to form compact skeleton structures in TiO2/SMPU when the TiO2 content is 3% by weight. Further, the used TiO2 is rutile phase, and lowers the SMPU crystallinity. The suitable TiO2 content can increase the absorptivity to UV light and enhance the reflectivity to visible light of TiO2/SMPU nanocomposites, lowering its photo-aging properties and prolonging its service life. Also, TiO2/SMPU shows a higher scattering intensity and a faster decreasing trend than SMPU due to the larger electron density difference between TiO2 and SMPU. The microphase separation and ordered structures in SMPU are decreased due to added TiO2 nanoparticles. There are electron density fluctuations at the interfaces between hard and soft phases in SMPU, and between SMPU and TiO2 nanoparticles. Finally, the prepared TiO2/SMPU nanocomposites have better shape memory effects and tensile properties when TiO2 content of 3% is proposed to synthesize TiO2/SMPU nanocomposites for practical engineering applications.Graphical abstractImage 1
       
  • Flexible and self-assembly anisotropic FeCo nanochain-polymer composite
           films for highly stretchable magnetic device
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Jie Yuan, Zhi-Quan Liu Magnetic field induced self-assembly is used to successfully fabricate flexible and anisotropic FeCo nanochain-PDMS composite films. The embedded nanochains are controllable in average length (
       
  • A novel approach to align carbon nanotubes via water-assisted shear
           stretching
    • Abstract: Publication date: 18 August 2018Source: Composites Science and Technology, Volume 164Author(s): Yingying Yu, Changhao Zhao, Qingwen Li, Jianying Li, Yuntian Zhu Floating catalyst chemical vapor deposition (FCCVD) can produce buckypaper, a kind of CNT film, at large-scale with low cost. However, individual CNTs in the buckypaper are mostly randomly oriented, which significantly limits their electrical and mechanical properties. Here we report an innovative approach, water-assisted shear stretching (WASS), which can significantly improve CNT alignments and consequently enhance the electrical and mechanical properties. In addition, we define a unique “alignment factor” to quantify the alignment degree, and to estimate the effect of alignment on the mechanical and electrical properties of CNT assemblies. The high mechanical strength and excellent electrical conductivity of the WASS-processed buckypaper enhance their potential for applications in new electronic technologies and high-strength lightweight aerospace structures.
       
  • Constructing continuous networks by branched alumina for enhanced thermal
           conductivity of polymer composites
    • Abstract: Publication date: Available online 12 July 2018Source: Composites Science and TechnologyAuthor(s): Yuge Ouyang, Guolin Hou, Liuyang Bai, Baoqiang Li, Fangli Yuan Efficient heat dissipation performance of thermal management materials has become one of the most critical challenges in the development of modern microelectronic devices. However, traditional polymer composites display limited enhancement of thermal conductivity even when highly loaded with thermally conductive fillers due to the lack of efficient heat conductive channels. In this study, branched alumina (b-Al2O3) is first used as the filler to improve thermal conductivity of phenolic resin (PR) and the preparation of the Al2O3 with branched structures is simple and high efficient. It is found that PR composites with b-Al2O3 present excellent thermal conductivity (up to 1.481 W m−1 K−1), which is equivalent to a dramatic enhancement of 7 times compared to neat matrix. The increased thermal conductivity should be attributed to that the branched structures of embedded b-Al2O3 particles tend to overlap each other and form continuous networks, which can act as efficient heat transfer pathways in PR matrix. Furthermore, PR composites with b-Al2O3 own improved thermal stability and decreased coefficient of thermal expansion (CTE) of 23 × 10−6 K−1 compared to neat PR (71 × 10−6 K−1). Meanwhile, composites with decreased dielectric loss tangent are achieved because of the incorporation of b-Al2O3, which is extraordinary and hopeful result for thermal management materials. This strategy provides an insight for the development of high-performance composites with potential to be used in electronic packages fields.
       
  • Improving thermal conductivity of polymer composites by reducing
           interfacial thermal resistance between boron nitride nanotubes
    • Abstract: Publication date: Available online 11 July 2018Source: Composites Science and TechnologyAuthor(s): Chenjie Fu, Qiang Li, Jibao Lu, Srikanth Mateti, Qiran Cai, Xiaoliang Zeng, Guoping Du, Rong Sun, Ying Chen, Jianbin Xu, Ching-Ping Wong Developing polymer composites with high thermal conductivity is a must to improve the thermal-management ability for modern electronic applications, in which power densities rapidly increase. Boron nitride nanotubes are one of the most promising fillers due to their high thermal conductivity and electrical insulator, but the overall thermal conductivity of the obtained polymer composites is limited by high interfacial thermal resistances. Here, we present an approach to reduce the interfacial thermal resistance between adjacent boron nitride nanotubes through low-melting effect of nanoscale silver particles. A sharp increase in thermal conductivity (20.9 Wm−1K−1) is observed in cellulose nanofibers (CNFs)/boron nitride nanotubes (BNNTs) composites, which is approximately 14.3 times larger than that of conventional polymers. The underlying mechanism is understood through Foygel model, and demonstrated that the interfacial thermal resistances play key role in the thermal conductivity. This strategy can become a quotable method for design and prepared of highly thermal conductivity materials in the future.
       
  • Dually self-reinforced Poly(ε-caprolactone) composites based on
           unidirectionally arranged fibers
    • Abstract: Publication date: Available online 9 July 2018Source: Composites Science and TechnologyAuthor(s): Lei Han, Bijia Wang, Yamin Dai, Yunchong Zhang, Hong Xu, Xiaofeng Sui, Linping Zhang, Yi Zhong, Zhiping Mao Dually self-reinforced Poly(ε-caprolactone) (PCL) composites were prepared to broaden its load-bearing applications as tissue engineering scaffolds. The composites were prepared from bi-component PCL yarns composed of self-nucleated PCL drawn fibers and PCL matrix by a combined process of yarns winding and hot pressing. Differential Scanning Calorimetry (DSC) results showed that incorporating of self-nucleating agents can improve the melting points of the fibers, creating a process temperature window for hot pressing. The orientation parameters of the fibers were accurately measured by Confocal Raman microscopy (CRM) and the results showed that the orientation parameter of the fibers could be up to 0.9 after drawn. Tensile tests showed that the self-nucleated drawn fibers had stronger mechanical properties than the control fibers with the same draw ratios. The hot pressing parameters (temperature and pressure) were also optimized during hot-pressing. The Young's modulus and break strength of the dually self-reinforced composites in longitudinal direction could be up to 118% and 400% higher than that of pristine PCL although their elongation at break decreased. Decline of mechanical properties of the composites in transverse direction was not observed, indicating good adhesion between the fibers and the matrix, which was confirmed by scanning electron microscope analysis.
       
  • Study on the interfacial properties of the dual-activity silicone
           resin/carbon fibers composites
    • Abstract: Publication date: Available online 7 July 2018Source: Composites Science and TechnologyAuthor(s): Tong Zhang, Jian Yang, Bo Jiang, Yudong Huang Dual-activity silicone resins (DASR) with double bonds and epoxy groups were prepared via the hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane (γ-GPS) and γ-methacryloxypropyltrimethoxysilane (γ-MPS). The hydrolysis and condensation degree was monitored during the preparation process of DASR. The epoxy groups of DASR were directly reacted with amine groups on the fiber surface attempting to improve the interfacial properties of carbon fiber (CF) composites. The CF/DASR composites represented a 36.91% and 20.85% enhancement in interfacial shear strength (IFSS), compared to those of MASR composites reinforced with untreated CFs and amine modified CF. In addition, the tensile strength of CF/DASR remained stable after the UV irradiation. Thus, these attractive results demonstrate that the designed dual-activity silicone resin/carbon fiber composites provide a promising approach for preparing high-performance carbon fibers composites.
       
  • Synergistic interfacial reinforcement of carbon fiber/polyamide 6
           composites using carbon-nanotube-modified silane coating on
           ZnO-nanorod-grown carbon fiber
    • Abstract: Publication date: Available online 7 July 2018Source: Composites Science and TechnologyAuthor(s): Byeong-Joo Kim, Sang-Hyup Cha, Kyungil Kong, Wooseok Ji, Hyung Wook Park, Young-Bin Park We report an experimental study on improvement of mechanical properties of a multiscale hybrid composite consisting of in-situ polymerized polyamide-6 and zinc oxide nanorod(ZnO NR)-grown woven carbon fiber (WCF) coated with carbon nanotube(CNT)-modified silane. The ZnO growth process and silane coating process were performed on the fiber surface, and then the composite was fabricated by ultra-fast (
       
  • Special issue on carbon nanotube composites
    • Abstract: Publication date: Available online 5 July 2018Source: Composites Science and TechnologyAuthor(s): Gregory M. Odegard, Richard Liang, Kristopher E. Wise
       
  • Towards quasi isotropic laminates with engineered fracture behaviour for
           industrial applications
    • Abstract: Publication date: Available online 4 July 2018Source: Composites Science and TechnologyAuthor(s): Gianmaria Bullegas, Jacob Benoliel, Pier Luigi Fenelli, Silvestre T. Pinho, Soraia Pimenta Carefully placed patterns of micro-cuts have been inserted in the microstructure of Cross-Ply (CP) and Quasi-Isotropic (QI) thin-ply CFRP laminates to engineer their translaminar fracture behaviour with the purpose of increasing their damage resistance under different loading conditions. A novel Finite Fracture Mechanics model has been developed to predict the translaminar crack propagation behaviour and to guide the microstructure design. This technique led to a 68% increase in the laminate notched strength, and a 460% increase in the laminate translaminar work of fracture during Compact Tension tests for CP laminates. It also allowed to achieve a 27% increase in the laminate notched strength, and a 189% increase in the translaminar work of fracture during Compact Tension tests for QI laminates. Furthermore, an increase of 43% in the total energy dissipated, and of 40% in maximum deflection at complete failure was achieved during quasi-static indentation tests on QI laminates. Given the significant improvements in the mechanical performance under different loading conditions, and the industrial relevance of QI laminates and the increasing industrial interest in thin-ply laminates, these results demonstrate that microstructure design can be used effectively to improve the damage tolerance of CFRP structures in industrially-relevant applications.
       
  • Multistable cantilever shells:Analytical prediction, numerical simulation
           and experimental validation
    • Abstract: Publication date: Available online 27 June 2018Source: Composites Science and TechnologyAuthor(s): Matteo Brunetti, Lukasz Kloda, Francesco Romeo, Jerzy Warminski The numerical and experimental validation of multistable behavior of cantilever shells is addressed. The design of the laminated composite shells is driven by a recently proposed semi-analytical shell model, whose predictions are verified and critically examined by means of finite element simulations and stability tests on two manufactured demonstrators. In addition, the influence of the main design parameters on the shells stability scenario is discussed. Despite its simplicity, the reduced model allows to depict a fairly faithful picture of the stability scenario; therefore, it proves to be a useful tool in the early design stages of morphing shell structures.
       
  • Surface modification of PBO fibers by direct fluorination and
           corresponding chemical reaction mechanism
    • Abstract: Publication date: Available online 21 June 2018Source: Composites Science and TechnologyAuthor(s): Longbo Luo, Dawei Hong, Lingjie Zhang, Zheng Cheng, Xiangyang Liu Due to their excellent mechanical properties and heat resistance, Poly(p-phenylene benzobisoxazole) (PBO) fibers are applied as one of most potential reinforcement in resin matrix composite. However, the poor adhesion with resin limits their application in advanced composite materials. In this study, PBO fibers were first modified by direct fluorination to improve the interface adhesion between fibers and resin. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to characterize the change of chemical structure and surface topography of fluorinated fibers. The results show that polar groups of C-F and -COOH are produced and surface roughness is enhanced, which increases the interface bonding strength of PBO fibers/epoxy by 48%. The fluorination reaction mechanism of PBO fibers is investigated on the basis of chemical structure change. It's suggested that oxazole ring reacts with fluorine gas preferentially over benzene ring, and addition reaction dominates when fluorine reacts with benzene ring.
       
  • Molecular engineering of interphases in polymer/carbon nanotube composites
           to reach the limits of mechanical performance
    • Abstract: Publication date: Available online 11 April 2018Source: Composites Science and TechnologyAuthor(s): Chandrani Pramanik, Dhriti Nepal, Michael Nathanson, Jacob R. Gissinger, Amanda Garley, Rajiv J. Berry, Amir Davijani, Satish Kumar, Hendrik Heinz After more than 50 years of development, carbon fiber composites exhibit an order of magnitude higher specific strength as compared to structural metals such as steel. However, the strength of the current state-of-the-art carbon fiber composites remains less than 10% of their theoretical value. Recent studies show that the polymer-carbon nanotube (CNT) interphase, i.e., the region of carbon components in contact with multiple organic components in its vicinity, plays a major role. Engineering the polymer-CNT interphase at the molecular level is a promising pathway to improve the mechanical properties of nano-composite materials on the way to fully realize the potential of mechanical properties of carbon nanotubes. Examples for using pristine and flattened CNTs, combinations of polymers, and surface grafting, as well as analogies to biological systems to prepare strong polymer/CNT composites are reviewed. In support of these developments, molecular simulations have revealed the binding mechanisms of polymers to CNTs and relationships to mechanical properties such as modulus, tensile strength, and interfacial shear strength in the interphase. Recent computational models enable increasingly quantitative predictions, and examples that explain the influence of the type of polymers, polymer crystallinity, carbon nanotubes, and nanotube surface modification on the interphase properties are discussed. The developments in molecular engineering of interphases by experiment and simulations advance rational composite design.
       
  • Microstructure evolution and self-assembling of CNT networks during
           mechanical stretching and mechanical properties of highly aligned CNT
           composites
    • Abstract: Publication date: Available online 4 April 2018Source: Composites Science and TechnologyAuthor(s): Claire Jolowsky, Rebekah Sweat, Jin Gyu Park, Ayou Hao, Richard Liang Using a floating catalyst synthesis process, carbon nanotubes (CNTs) can be produced to form randomly oriented networks. However, to realize their potential high structural performance, the nanotubes must be aligned and closely packed to eliminate molecular and microscale defects, which would be similar to carbon fiber microstructures. This paper describes a mechanical stretching technique using bismaleimide (BMI) resin to transform the randomly oriented networks into aligned networks. The BMI resin acts as a lubricant to decrease the friction between the nanotube bundles within the network during the stretching process. The unique flattening and self-assembling behaviors and the resultant graphitic crystal packing of CNTs were observed. The nanotubes' degree of alignment, measured by Raman and X-ray scattering drastically increased at approximately 40% stretch strain, plateaued at a 60% stretch strain, and achieved a maximum of 0.92 degree of alignment with noticeable graphitic crystal packing at 80% stretch strain. Both TEM and SEM observations indicate that as the stretch strain increased, the CNTs started to align along the stretched direction and self-assembled into large bundles. Additionally, high-resolution TEM analysis indicated that the CNTs exhibited flattening and polygonization self-assembling to form graphitic crystal packing. Tensile testing on the stretched CNT/BMI composite samples revealed an increase in Young's modulus, with a maximum of 252 GPa at 80% stretch strain, while an ultimate tensile strength of 1.58 GPa was reached at 70% stretch strain. The high degree of alignment and polygonization packing resulted in a better load transfer among CNTs, and thus a higher mechanical performance in the resultant CNT composites. Furthermore, this stretching process is scalable and has the potential to realize greater performance for applications using CNTs.
       
  • Machine learning electron density in sulfur crosslinked carbon nanotubes
    • Abstract: Publication date: Available online 29 March 2018Source: Composites Science and TechnologyAuthor(s): John M. Alred, Ksenia V. Bets, Yu Xie, Boris I. Yakobson Mechanical strengthening of composite materials that include carbon nanotubes (CNT) requires strong inter-bonding to achieve significant CNT-CNT or CNT-matrix load transfer. The same principle is applicable to the improvement of CNT bundles and calls for covalent crosslinks between individual tubes. In this work, sulfur crosslinks are studied using a combination of density functional theory (DFT) and classical molecular dynamics (MD). Atomic chains of at least two sulfur atoms or more are shown to be stable between both zigzag and armchair CNTs. All types of crosslinked CNTs exhibit significantly improved load transfer. Moreover, sulfur crosslinks show evidence of a cooperative self-healing mechanism allowing for links to rebond once broken leading to sustained load transfer under shear loading. Additionally, a general approach for utilizing machine learning for assessing the ground state electron density is developed and applied to these sulfur crosslinked CNTs.
       
  • Multiscale modeling of photomechanical behavior of photo-responsive
           nanocomposite with carbon nanotubes
    • Abstract: Publication date: Available online 27 March 2018Source: Composites Science and TechnologyAuthor(s): Junghwan Moon, Hyunseong Shin, Kyungmin Baek, Joonmyung Choi, Maenghyo Cho We propose a scale-bridging methodology to link the microscopic photoreaction of an azobenzene-containing liquid crystalline polymer (LCP) and the macroscopic interfacial and elastic properties of carbon nanotube (CNT)-reinforced photo-responsive nanocomposites. The photo-isomerization of the azobenzene moieties is described by implementing a photo-switching potential that represents the light-excited energy transition path. The relevant time evolution of the molecular shape and the concurrent changes in the interfacial morphology are observed using molecular dynamics (MD) simulations. Finally, the effective elastic properties of the photo-responsive polymer (PRP) nanocomposite with respect to the isomerization ratio are numerically derived using the micromechanics-based homogenization method. It is verified that the size of the CNT and the photo-deformation of the azobenzene molecules influence the intermolecular interactions and the nematic phase of the LCP at the interfacial region. The continuum-scale finite element (FE) model, which reflects the microscopic information, clearly predicts the reinforcing effect of the CNT filler on the elastic properties of the composite and their variation under photo-actuation. We expect our results to shed light on designing the photomechanical energy conversion efficiency of nano-sized soft actuators composed of CNT-reinforced composites.
       
  • Mesoscopic modeling of the uniaxial compression and recovery of vertically
           aligned carbon nanotube forests
    • Abstract: Publication date: Available online 14 March 2018Source: Composites Science and TechnologyAuthor(s): Bernard K. Wittmaack, Alexey N. Volkov, Leonid V. Zhigilei Vertically aligned carbon nanotube (VACNT) arrays or “forests” represent a promising class of mechanically strong and resilient lightweight materials, capable of supporting large reversible deformation and absorbing mechanical energy. The mechanical response of VACNT forests to uniaxial compression is defined by various factors, including the material microstructure, its density, height, rate of deformation, and the nature of interaction between carbon nanotubes (CNTs) and the compressing indenter. In this paper, we use a coarse-grained mesoscopic model to simulate the uniaxial compression of VACNT samples with different densities and microstructures (bundle size distribution and degree of nanotube alignment) to obtain a clear microscopic picture of the structural changes in networks of interconnected CNT bundles undergoing mechanical deformation. The key factors responsible for the coordinated buckling of CNTs, reversible and irreversible modes of deformation in VACNT arrays undergoing uniaxial compression, as well as hysteresis behavior in VACNT arrays subjected to five loading–unloading cycles are investigated in the simulations. The simulation results reveal the important role of the collective buckling of CNTs across bundle cross-sections as well as a complex deformation behavior of VACNT arrays defined by an interplay of different modes of bundle deformation. The loading rate and the CNT attachment to the indenter are found to have a strong effect on the deformation mechanisms and the overall mechanical behavior of VACNT forests. A good agreement with experimental data from in situ mechanical tests is observed for the general trends and magnitudes of loss coefficients predicted in the simulations. The forest morphology can strongly alter the mechanical behavior of VACNT arrays with nominally the same general characteristics, such as CNT radius, length, and material density, thus suggesting the opportunity for substantial enhancement of the mechanical properties through the microstructure modification.
       
  • Grafting carbon nanotubes onto carbon fibres doubles their effective
           strength and the toughness of the composite
    • Abstract: Publication date: Available online 14 March 2018Source: Composites Science and TechnologyAuthor(s): Luca Lavagna, Daniele Massella, Maria F. Pantano, Federico Bosia, Nicola M. Pugno, Matteo Pavese Bioinspiration can lead to exceptional mechanical properties in a number of biological materials as a result of their internal structure. In particular, the hierarchical arrangement of nano-to macro-components can bring to complex energy dissipation mechanisms and unprecedented resistance to crack growth. In this work, we propose to exploit this approach, combining in a multiscale composite structure carbon nanotubes with conventional carbon fibre reinforcements in a polyvinyl butyral matrix. We show that grafting the nanotubes onto the carbon microfibres improves their interface properties with the matrix considerably, effectively doubling their apparent strength. At the same time, the addition of nanotubes to microfibre reinforcements helps to improve the composite toughness, reaching more than twice the value for the conventional, non-hierarchically reinforced composite. Numerical simulations and fracture mechanics considerations are also provided to interpret the results.
       
  • Multiscale modeling of carbon fiber/carbon nanotube/epoxy hybrid
           composites: Comparison of epoxy matrices
    • Abstract: Publication date: Available online 9 March 2018Source: Composites Science and TechnologyAuthor(s): M.S. Radue, G.M. Odegard This study addresses the multiscale modeling of hybrid composites composed of carbon fibers (CFs), carbon nanotubes (CNTs), and three different epoxy systems (di-, tri-, and tetra-functional resin epoxies). Molecular dynamics (MD) simulations are performed to predict the molecular-level interfacial and mechanical behavior of CNT embedded in epoxy. Micromechanics calculations are implemented to translate the molecular phenomena observed to predict the mechanical properties of CNT/epoxy composites with randomly oriented CNTs and CF/CNT/epoxy systems with aligned CFs and randomly oriented CNTs. The model is validated with experimental Young's modulus values for CNT/epoxy available in the literature. The results demonstrate that the tri- and tetra-functional resin epoxies demonstrate comparably high moduli over the di-functional resin for CNT concentrations up to 5 wt%. For higher CNT loadings, the tri-functional resin epoxy is predicted to outperform the other resins with respect to stiffness due to its strong interaction with CNTs and high bulk stiffness.
       
  • Strong process-structure interaction in stoveable poly(urethane-urea)
           aligned carbon nanotube nanocomposites
    • Abstract: Publication date: Available online 3 March 2018Source: Composites Science and TechnologyAuthor(s): Jeffrey L. Gair, Robert H. Lambeth, Daniel P. Cole, Dale L. Lidston, Itai Y. Stein, Estelle Kalfon-Cohen, Alex J. Hsieh, Hugh A. Bruck, Mark L. Bundy, Brian L. Wardle The exceptional static and dynamic physical properties of poly(urethane-urea) (PUU) elastomers make them prime candidates for impulsive loading structural applications, such as blast protection coatings. Since the theoretical physical properties of carbon nanotubes (CNTs) are among the best for any currently known material, a number of previous studies explored the use of CNTs as nanoscale fillers to enhance the properties of PUU nanocomposites. However, due to the challenges inherent in dispersing CNTs in a PUU matrix and the resulting random orientation of the CNTs, these previous works observed marginal improvements in physical properties, and were unable to establish clear structure-property relations. Here, we report the synthesis of aligned-CNT (A-CNT) reinforced PUU polymer nanocomposites (A-PNCs) by infusing A-CNT forests with a stoveable PUU, and establish process-structure-property relations that quantify the contribution of CNT confinement on the PUU mechanical response. This stoveable process was achieved using blocked isocyanate which prevented polymerization until the blocks were removed with heat. PUUs of two distinct compositions were explored: one with 40 wt% hard-segment content (PUU211) and the other with 66 wt% hard-segment content (PUU541). Thermogravimetric analysis indicates that A-CNTs enhance the thermal stability of the hard-segment phase in PUU A-PNCs at 340 °C by up to 45% over the baseline PUUs. Atomic force microscopy reveals that the elongated nanophase hard-segment formations along the CNT axis observed only in the nanocomposites were of similar characteristic size to the average inter-A-CNT spacing (∼70 nm), indicating a strong influence of A-CNTs on the size and orientation of hard-segment nanophases, as corroborated via small angle X-ray scattering. Nanoindentation testing reveals that PUU A-PNCs possess significant elastic anisotropy, and exhibit enhanced longitudinal effective indentation moduli of ∼460 MPa (>3 × that of the PUU211 baseline) and ∼1350 MPa (∼1.5 × that of the PUU541 baseline) for PUU211 and PUU541 nanocomposites, respectively. This difference in magnitude of CNT reinforcement efficacy indicates that CNT confinement leads to significant hard-segment re-organization in the PUU211 A-PNCs, whereas the interconnected network of hard-segments in the PUU541 is affected by CNT templating to a lesser extent. Dynamic nanoindentation testing results are consistent with these interpretations, where longitudinally-loaded PUU211 A-PNCs are found to exhibit a>3 × enhancement in storage modulus at 1 Hz of ∼730 MPa, whereas the longitudinally-loaded PUU541 A-PNCs exhibit a slightly enhanced storage modulus enhancement at 1 Hz of 2190 MPa (∼1.5 × that of the PUU541 baseline). Reinforcement of PUUs with A-CNTs is a promising way to tune the physical properties of the PNCs; higher A-CNT packing densities, where the inter-CNT spacing could approach the nanophase characteristic diameter, could further enhance the PUU performance in ballistic protection applications.
       
  • Advanced carbon fiber composite out-of-autoclave laminate manufacture via
           nanostructured out-of-oven conductive curing
    • Abstract: Publication date: Available online 26 February 2018Source: Composites Science and TechnologyAuthor(s): Jeonyoon Lee, Xinchen Ni, Frederick Daso, Xianghui Xiao, Dale King, Jose Sánchez Gómez, Tamara Blanco Varela, Seth S. Kessler, Brian L. Wardle Next-generation composite manufacturing processes are needed to overcome several limitations of conventional manufacturing processes (e.g., high energy consumption). Here we explore, via experiments and modeling, the characteristics of the newly developed out-of-oven (OoO) curing technique that cures a composite laminate via resistive heating of a carbon nanotube film. When compared to oven curing of an aerospace-grade out-of-autoclave (OoA) carbon fiber prepreg advanced composite laminate, the OoO curing reduces energy consumption by over two orders of magnitude (14 vs. 0.1 MJ). Thermophysical and mechanical tests including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), short beam shear (SBS), and ex-situ and in-situ double-edge notch tension (DENT) indicate that the physical and mechanical properties of OoO-cured laminates are equivalent to those of oven-cured (baseline) laminates. In addition to energy savings, the OoO curing process has the potential to reduce part-to-part variations through improved spatiotemporal temperature control.
       
  • Mechanical behavior of carbon nanotube yarns with stochastic
           microstructure obtained by stretching buckypaper
    • Abstract: Publication date: Available online 16 February 2018Source: Composites Science and TechnologyAuthor(s): A. Sengab, R.C. Picu The development of yarns composed primarily from carbon nanotubes (CNTs) has been pursued recently with the intent of transferring to the yarn the exceptional mechanical and transport properties of individual nanotubes. In this work we study the process of yarn formation by dry stretching buckypaper, and the mechanical behavior of the resulting yarns, function of the CNT length and of the state of the CNT assembly before stretching. The analysis is performed using a coarse grained, bead-spring representation for individual CNTs. It begins with a random buckypaper structure composed from CNTs of diameter 13.5 Å. This structure is stretched to form a yarn. This occurs once the stretch ratio becomes larger than a threshold which depends on the CNT length. At the threshold, adhesion stabilizes a highly aligned packing of CNT bundles. Packing defects and pores, reminiscent of the initial structure of the buckypaper, are incorporated in the yarn. The yarn is further tested in uniaxial tension. The defects have little effect on the mechanical behavior of the resulting yarns. However, the behavior depends sensitively on the degree of packing of the CNTs in the sub-bundles forming the yarn. Therefore, the initial structure of the buckypaper has little effect on the performance of the yarn. Increasing the CNT length increases the yarn flow stress and this is associated with the residual tortuosity of the CNTs in the yarn. Decreasing the temperature or increasing the strain rate lead to a small increase of the flow stress. These results have implications for yarn design, which are discussed in the article.
       
  • How can we make carbon nanotube yarn stronger'
    • Abstract: Publication date: Available online 15 February 2018Source: Composites Science and TechnologyAuthor(s): Yeonsu Jung, Young Shik Cho, Jae Won Lee, Jun Young Oh, Chong Rae Park There has been remarkable progress with regard to the fabrication of yarns based on high-performance carbon nanotubes (CNTs). However, the theoretically predicted tensile strength of CNTs has yet to be realized in practical CNT yarns or CNT-reinforced composites. Having considered that there are few systematic guidelines for preparing high-strength CNT yarns, we attempted to revisit the-state-of-the-art progress in the theories and yarn formation processes of CNT yarns and then draw possible correlations between the intrinsic and extrinsic structural parameters of elementary CNTs, yarn formation processes and the tensile strength of the resulting CNT yarns. On the basis of these considerations and discussions of advanced technologies and theoretical approaches, possible routes to improve the strength of CNT yarns further are suggested.
       
  • Simulating the effects of carbon nanotube continuity and interfacial
           bonding on composite strength and stiffness
    • Abstract: Publication date: Available online 14 February 2018Source: Composites Science and TechnologyAuthor(s): Benjamin D. Jensen, Gregory M. Odegard, Jae-Woo Kim, Godfrey Sauti, Emilie J. Siochi, Kristopher E. Wise Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred either directly between CNTs or through the matrix, a mechanism that is absent in simulations of effectively continuous CNTs. In this study, the elastic and fracture properties of high volume fraction discontinuous carbon nanotube/amorphous carbon composite systems were compared to those of otherwise equivalent continuous CNT composites using ReaxFF reactive molecular dynamics simulations. The simulation results quantify the dependence of composite mechanical properties on the number of nanotube-matrix interfacial covalent bonds. Furthermore, the mechanical impact of interfacial bonding was decomposed to reveal its effect on the properties of the CNTs, the interfacial layer of matrix, and the bulk matrix. For the composites with continuous reinforcement, it was found that any degree of interfacial bonding has a negative impact on axial tensile strength and stiffness. This is due to disruption of the structure of the CNTs and interfacial matrix layer by the interfacial bonds. For the discontinuous composites, the modulus was maximized between 4% and 7% interfacial bonding and the strength continued to increase up to the highest levels of interfacial bonding studied. Areas of low stress and voids were observed in the simulated discontinuous composites at the ends of the tubes, from which fracture was observed to initiate. Experimental carbon nanotube yarn composites were fabricated and tested. The experimental results illustrate the knockdown factors that reduce composite mechanical properties relative to those of the tubes themselves.
       
  • Mechanical enhancement effect of the interlayer hybrid CNT film/carbon
           fiber/epoxy composite
    • Abstract: Publication date: Available online 10 February 2018Source: Composites Science and TechnologyAuthor(s): Tianshu Li, Min Li, Yizhuo Gu, Shaokai Wang, Qingwen Li, Zuoguang Zhang Floating catalyst chemical vapor deposition carbon nanotube (CNT) film was intercalated into carbon fiber (CF) prepregs to fabricate hybrid composites. The effect of CNT film thickness was studied by using a 25 μm thick film and an ultrathin 2 μm film respectively. The results showed that the ultrathin CNT film interlayer had dramatically improved the compression strength of hybrid composite by 34% compared with CF/epoxy control composite owing to the altered failure modes. The damping ratio of ultrathin CNT film hybridized composite was substantially increased by two orders of magnitude, due to the energy dissipation of numerous nanoscale interconnections and interfaces. Moreover, the interlaminar properties and water resistance of the hybrid composites were all improved. Since a small amount of CNT film can significantly enhance the mechanical properties of CF/epoxy composite, this type of hybrid composite has potential application in multifunctional lightweight structures.
       
  • Nitrile butadiene rubber composites reinforced with reduced graphene oxide
           and carbon nanotubes show superior mechanical, electrical and icephobic
           properties
    • Abstract: Publication date: Available online 2 February 2018Source: Composites Science and TechnologyAuthor(s): L. Valentini, S. Bittolo Bon, M. Hernández, M.A. Lopez-Manchado, N.M. Pugno In this article, we examine the effects of two different nanostructured carbons when they are incorporated in a rubber matrix in terms of mechanical and electrical properties as well as the icephobic behaviour of the nanocomposites when swollen. Nitrile butadiene rubber composites reinforced with thermally reduced graphene oxide or multiwalled carbon nanotubes or both of them were prepared and characterized. At a particular hybrid filler loading, tensile and electrical tests showed a significant improvement of the composite. From the swelling studies, after the immersion, the nanocomposites experienced a reduction of the cross-link density that promotes weakening of ice adhesion, being this effect more evident for those samples prepared with hybrid fillers. In view of the composite formulations, that utilize commercially available elastomers and fillers, these findings would be applicable to the automotive and aviation sectors, where the demand for multifunctional rubbers is increasing.
       
  • Computer-aided design of three terminal (3T-) zig-zag SWCNT junctions and
           nanotube architectures
    • Abstract: Publication date: Available online 31 January 2018Source: Composites Science and TechnologyAuthor(s): Sushan Nakarmi, Vinu U. Unnikrishnan, Vikas Varshney, Ajit K. Roy Construction of topologically accurate models of nanotube junctions is essential for the determination of its thermal, mechanical and electronic properties. Most of the earlier nanotube junction models have been based on molecular dynamics (MD) simulations and heuristic methods which are either computationally expensive or impossible to model large 3D structures. CAD based approach that uses triangular meshes with remeshing strategies and have desired mesh optimization capability are found to be ideal to generate 3T-nanotube junctions with generic predefined orientation of nanotubes and accurate topological features. These 3T-junctions can be considered as building blocks and can be replicated in multiple directions to build complex nanotube architectures, which are shown via two examples for generating 2D and 3D microstructures by replication, translation, and rotation of a fused 3T-junction.
       
  • Quantized prediction of coefficients of thermal expansion of 3-D
           CNT-Graphene junctioned carbon nanostructures
    • Abstract: Publication date: Available online 10 January 2018Source: Composites Science and TechnologyAuthor(s): Sangwook Sihn, Ajit K. Roy, Barry L. Farmer A computational finite element analysis based on a structural molecular mechanics approach was conducted to predict effective coefficients of thermal expansion (CTE) of a novel three-dimensional carbon nanostructure, pillared graphene structure (PGS), which is constituted with several graphene sheets and single-walled carbon nanotubes. Four sets of representative unitcell models were developed atomistically having different geometric parameters of pillar length and inter-pillar distance in the PGS. Periodic boundary conditions were applied to periodic unitcell geometries to yield consistent results. Parametric study shows that both pillar length and inter-pillar distance significantly affect the effective in-plane and through-thickness CTEs. The PGS with smaller inter-pillar distance and larger pillar length yields higher in-plane CTEs, while that with larger inter-pillar distance and smaller pillar length yields higher through-thickness CTE. The calculation yields negative through-thickness CTE at low temperatures (T
       
  • Synergetic effects of thin plies and aligned carbon nanotube interlaminar
           reinforcement in composite laminates
    • Abstract: Publication date: Available online 9 January 2018Source: Composites Science and TechnologyAuthor(s): Estelle Kalfon-Cohen, Reed Kopp, Carolina Furtado, Xinchen Ni, Albertino Arteiro, Gregor Borstnar, Mark N. Mavrogordato, Ian Sinclair, S. Mark Spearing, Pedro P. Camanho, Brian L. Wardle Thin-ply carbon fiber laminates have exhibited superior mechanical properties, including higher initiation and ultimate strength, when compared to standard thickness plies and enable greater flexibility in laminate design. However, the increased ply count in thin-ply laminates also increases the number of ply-ply interfaces, thereby increasing the number of relatively weak and delamination-prone interlaminar regions. In this study, we report the first experimental realization of aligned carbon nanotube interlaminar reinforcement of thin-ply unidirectional prepreg-based carbon fiber laminates, in a hierarchical architecture termed ‘nanostitching’. We synthesize a baseline effective standard thickness laminate using multiple thin-plies of the same orientation to create a ply block, and we find an ∼15% improvement in the interlaminar shear strength via short beam shear (SBS) testing for thin-ply nanostitched samples when compared to the baseline. This demonstrates a synergetic strength effect of nanostitching (∼5% increase) and thin-ply lamination (∼10% increase). Synchrotron-based computed tomography of post mortem SBS specimens suggests a different damage trajectory and mode of damage accumulation in nanostitched thin-ply laminates, notably the complete suppression of delaminations in the nanostitched region. Finite element predictions of damage progression highlight the complementary nature of positive thin-ply and nanostitching effects that are consistent with an ∼15% improvement in Modes I and II interlaminar fracture toughness due to the aligned carbon nanotubes at the thin-ply interfaces.
       
 
 
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